32
Steel Design Guide
Design of Modular Steel-Plate
Composite Walls for SafetyRelated Nuclear Facilities
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32
Steel Design Guide
Design of Modular Steel-Plate
Composite Walls for SafetyRelated Nuclear Facilities
Saahastaranshu R. Bhardwaj
Amit H. Varma
A M ERICAN INST I T UT E OF S T E E L CONS T RUC T I O N
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© AISC 2017
by
American Institute of Steel Construction
All rights reserved. This book or any part thereof
must not be reproduced in any form without the
written permission of the publisher.
The AISC logo is a registered trademark of AISC.
The information presented in this publication has been prepared following recognized principles
of design and construction. While it is believed to be accurate, this information should not be
used or relied upon for any specific application without competent professional examination and
verification of its accuracy, suitability and applicability by a licensed engineer or architect. The
publication of this information is not a representation or warranty on the part of the American
Institute of Steel Construction, its officers, agents, employees or committee members, or of any
other person named herein, that this information is suitable for any general or particular use, or
of freedom from infringement of any patent or patents. All representations or warranties, express
or implied, other than as stated above, are specifically disclaimed. Anyone making use of the
information presented in this publication assumes all liability arising from such use.
Caution must be exercised when relying upon standards and guidelines developed by other bodies
and incorporated by reference herein since such material may be modified or amended from time
to time subsequent to the printing of this edition. The American Institute of Steel Construction
bears no responsibility for such material other than to refer to it and incorporate it by reference at
the time of the initial publication of this edition.
Printed in the United States of America
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Authors
Saahastaranshu R. Bhardwaj is a Ph.D. candidate in the Lyles School of Civil Engineering at Purdue University. Mr. Bhardwaj
assisted Dr. Varma with the writing, editing and formatting of the steel-plate composite wall design provisions and commentary
in Appendix N9 of ANSI/AISC N690. Mr. Bhardwaj and Dr. Varma collaborated with several industry practitioners to develop
the design examples presented in this Guide.
Amit H. Varma, Ph.D, is a Professor in the Lyles School of Civil Engineering and a University Faculty Scholar at Purdue University. Dr. Varma served as the Vice Chair of AISC Task Committee 12, Nuclear Facilities Design, that developed the supplement to the AISC Specification for Safety-Related Steel Structures for Nuclear Facilities, ANSI/AISC N690 (AISC, 2015) for
modular composite construction. He is currently a member of the AISC Committee on Specifications (COS), AISC Task Committee 5, Composite Design, and the Chair of the AISI/AISC Fire Committee. He served as the Chair of the SEI/ACI Committee
of Composite Construction from 2010 to 2016.
Acknowledgments
This Design Guide would be incomplete and inadequate without valuable input from the following individuals. The authors
would like to thank Dr. Sanjeev Malushte for his significant intellectual and engineering contributions to the completion of
the Supplement to ANSI/AISC N690 and this Design Guide. The copyright images in the Design Guide are reprinted with the
permission of Westinghouse Electric Company, LLC, and its contribution is appreciated. The authors are also grateful to the following reviewers of the document for their valuable comments.
Taha Alshawaf
Steve Ashton
Michel Bruneau
Shu-Jin Fang
Lou Geschwindner
Jay Harris
Chris Hewitt
Mark Holland
Ron Janowiak
Wonki Kim
Davis Parsons
Matthew Van Liew
Derek Winkler
Preface
This Guide is intended to facilitate the design of steel-plate composite (SC) walls for safety-related nuclear facilities and is to
be used in conjunction with ANSI/AISC N690. The Guide discusses the behavior and design of SC walls subjected to various
demands, including both individual and combined force demands. The detailing, analysis and design of SC walls and connections are based on the provisions in Appendix N9 of ANSI/AISC N690. The design of SC walls and connections is illustrated in
a design example in Appendix A.
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TABLE OF CONTENTS
CHAPTER 1 INTRODUCTION . . . . . . . . . . . . . . . . . 1
7.6
1.1
1.2
7.7
1.3
1.4
BACKGROUND . . . . . . . . . . . . . . . . . . . . . . 1
ADVANTAGES OF SC WALLS . . . . . . . . . . . . 3
1.2.1 Resilience and Sustainability Aspects of
SC Construction . . . . . . . . . . . . . . . . . 4
LIMITATIONS OF SC WALLS . . . . . . . . . . . . 9
APPENDIX N9 TO ANSI/AISC N690 . . . . . . . 10
CHAPTER 8 INDIVIDUAL DESIGN AVAILABLE
STRENGTHS . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
8.1
8.2
8.3
CHAPTER 2 SCOPE AND LAYOUT . . . . . . . . . . . . 11
2.1
DESIGN EXAMPLE . . . . . . . . . . . . . . . . . . 11
8.4
8.5
CHAPTER 3 MINIMUM REQUIREMENTS . . . . . 13
CHAPTER 4 FACEPLATE SLENDERNESS
REQUIREMENT . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1
5.1
5.2
9.2
CLASSIFICATION OF STEEL ANCHORS . . . 17
SPACING OF STEEL ANCHORS . . . . . . . . . 17
5.2.1 Development Length . . . . . . . . . . . . . 17
5.2.2 Interfacial Shear . . . . . . . . . . . . . . . . 19
CHAPTER 11 DESIGN OF SC
WALL CONNECTION . . . . . . . . . . . . . . . . . . . 51
CLASSIFICATION AND SPACING
OF TIES . . . . . . . . . . . . . . . . . . . . . . . . . . 21
6.1.1 Transfer Length . . . . . . . . . . . . . . . . . 21
REQUIRED TENSILE STRENGTH
OF TIES . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1
11.2
11.3
CHAPTER 7 MODELING PARAMETERS FOR
ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1
7.2
7.3
7.4
7.5
INTERACTION OF OUT-OF-PLANE SHEAR
FORCES . . . . . . . . . . . . . . . . . . . . . . . . . . 43
IN-PLANE FORCES AND OUT-OF-PLANE
MOMENTS . . . . . . . . . . . . . . . . . . . . . . . . 43
CHAPTER 10 DEMAND CAPACITY RATIOS AND
INTERACTION SURFACES . . . . . . . . . . . . . . . 49
CHAPTER 6 TIE DETAILING . . . . . . . . . . . . . . . . . 21
6.2
UNIAXIAL TENSILE STRENGTH . . . . . . . . 37
COMPRESSIVE STRENGTH . . . . . . . . . . . . 37
OUT-OF-PLANE FLEXURAL
STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . 38
IN-PLANE SHEAR STRENGTH . . . . . . . . . . 38
OUT-OF-PLANE SHEAR STRENGTH . . . . . . 39
CHAPTER 9 INTERACTION OF DESIGN
AVAILABLE STRENGTHS . . . . . . . . . . . . . . . 43
CHAPTER 5 STEEL ANCHOR DETAILING . . . . . 17
6.1
INTERIOR AND CONNECTION
REGIONS . . . . . . . . . . . . . . . . . . . . . . . . . 35
REQUIRED STRENGTH
DETERMINATION . . . . . . . . . . . . . . . . . . . 36
LOADS AND LOAD COMBINATIONS . . . . . 27
GEOMETRIC AND MATERIAL PROPERTIES
FOR ANALYSIS . . . . . . . . . . . . . . . . . . . . . 27
STIFFNESS VALUES FOR THE MODEL . . . . 28
7.3.1 Effective Flexural Stiffness . . . . . . . . . 28
7.3.2 Effective In-Plane Shear Stiffness . . . . . 29
MODELING THE OPENINGS . . . . . . . . . . . 31
7.4.1 Design and Detailing Requirements
Around Small Openings . . . . . . . . . . . 31
7.4.2 Design and Detailing Requirements
Around Large Openings . . . . . . . . . . . 32
7.4.3 Bank of Small Openings . . . . . . . . . . . 33
ANALYSIS INVOLVING ACCIDENT
THERMAL LOADS . . . . . . . . . . . . . . . . . . . 33
11.4
11.5
11.6
11.7
CONNECTION DEMAND TYPES . . . . . . . . 52
FORCE TRANSFER MECHANISM . . . . . . . . 52
CONNECTION DESIGN PHILOSOPHY AND
REQUIRED STRENGTH . . . . . . . . . . . . . . . 52
11.3.1 Full-Strength Connection Design . . . . . 52
11.3.2 Overstrength Connection Design . . . . . . 54
11.3.3 Connection Evaluation for
Combined Forces . . . . . . . . . . . . . . . . 54
CONNECTION AVAILABLE STRENGTH . . . 54
11.4.1 Connector Available Strength . . . . . . . . 54
SC WALL-TO-BASEMAT ANCHORAGE
CONNECTION . . . . . . . . . . . . . . . . . . . . . . 55
11.5.1 Single Base Plate Connection . . . . . . . . 55
11.5.2 Split Base Plate Connection . . . . . . . . . 58
11.5.3 Rebar SC Wall-to-Basemat
Connection . . . . . . . . . . . . . . . . . . . . 58
SC WALL-TO-WALL
JOINT CONNECTION . . . . . . . . . . . . . . . . . 60
RC SLAB-TO-SC WALL
JOINT CONNECTION . . . . . . . . . . . . . . . . . 61
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CHAPTER 12 IMPACTIVE AND IMPULSIVE
LOADS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
APPENDIX A: DESIGN EXAMPLE . . . . . . . . . . . . . . 79
SYMBOLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129
CHAPTER 13 FABRICATION, ERECTION AND
CONSTRUCTION REQUIREMENTS . . . . . . 73
13.1
ACRONYMS AND ABBREVIATIONS . . . . . . . . . . . 135
DIMENSIONAL TOLERANCES FOR
FABRICATION . . . . . . . . . . . . . . . . . . . . . . 73
REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137
CHAPTER 14 QUALITY ASSURANCE AND
QUALITY CONTROL REQUIREMENTS . . . 77
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Chapter 1
Introduction
Nuclear structures involve heavy concrete construction to
provide adequate radiation shielding and resistance to severe
and extreme loads. This results in longer construction durations and large field labor requirements. Generic modular
construction, especially modular steel-plate composite (SC)
construction, can minimize schedule and labor requirements. In SC construction, concrete walls are reinforced
with two steel faceplates attached to concrete using steel
anchors, such as steel headed stud anchors, and connected to
each other using steel tie bars. Figure 1-1 illustrates a typical
SC wall section. Steel anchors ensure composite behavior
of faceplates and concrete. Ties provide structural integrity,
prevent delamination of the plain concrete core, and serve
as shear reinforcement. The SC walls may have sleeves for
penetrations and embed plates for commodity attachments.
The behavior of SC walls under axial tension and compression (Zhang et al., 2014), out-of-plane flexure (Sener et
al., 2015b), and out-of-plane shear (Sener and Varma, 2014;
Sener et al., 2016) is similar to that of reinforced concrete
(RC) walls. However, behavior of SC walls under in-plane
shear (Seo et al., 2016; Varma et al., 2011e; Ozaki et al.,
2004), combined in-plane forces, and out-of-plane moments
(Varma et al., 2014) can be significantly different from that
of RC walls. Additionally, specific limit states such as faceplate local buckling (Zhang et al., 2014), interfacial shear
failure (Sener and Varma, 2014; Sener et al., 2016) between
the faceplates and concrete infill, and section delamination
through the concrete infill (Bhardwaj et al., 2017) need to
be adequately considered in the design of SC walls. These
limit states are discussed in Chapters 3 through 6, along with
section detailing provisions to prevent them from limiting
the design.
1.1
BACKGROUND
The initial application of SC walls was in non-nuclear commercial projects to resist extreme events in large concrete
structures. SC walls were expected to provide better resistance to extreme blast and earthquake events. Other nonnuclear applications of SC walls included submerged tube
tunnels (Narayanan et al., 1987), offshore oil rigs (Adams
and Zimmerman, 1987), and ship building (Dai and Liew,
2006). The need for construction schedule reduction and
better constructability and performance aspects of SC walls
in comparison to RC walls led to the consideration of their
use in safety-related nuclear facilities (Schlaseman and
Russell, 2004).
Some of the early studies on nuclear power plant type
structures composed of SC walls were conducted in Japan.
For example, the seismic behavior of a containment internal structure (CIS) composed entirely of SC walls was
evaluated experimentally by testing a 1 10 -scale model of
the entire structure by Akiyama et al. (1989). The structure
was subjected to a cyclic loading history with load control
cycles in the elastic range and displacement control cycles
in the inelastic range. The cyclic response of the structure
included events such as concrete cracking, steel yielding,
local buckling, shear buckling, and eventual fracture failure of the steel plates. The cyclic lateral load displacement
responses and hysteresis loops indicated that the structure
had excellent stiffness, strength and ductility. The equivalent
viscous damping factor, obtained from the hysteresis loops,
was about 5% before steel yielding, and increased significantly thereafter due to yielding and inelasticity. Sener et
al. (2015a) recently developed and verified a 3D nonlinear
inelastic finite element model of the 1 10 -scale test structure.
They used the model to predict, further evaluate and gain
insight into the seismic response of the SC structure. Both
the experimental and numerical results confirmed that the
seismic response including the stiffness, strength and drift
capacity were governed by the in-plane shear behavior and
corresponding concrete cracking and yielding of the steel
plates of the SC walls. The lateral load ultimate strength was
governed by the in-plane shear strength and failure of the
SC walls parallel to the lateral loading direction. The final
fracture occurred in regions where transverse shear reinforcement—web plates—in the SC walls were discontinued
abruptly. The overturning moment at the base also contributed to inelastic deformations with extensive concrete cracking and yielding in the SC walls at the exterior outer regions
of the CIS.
Akiyama et al. (1989) compared the cyclic response of the
SC structure with that of an equivalent RC structure that had
been tested earlier using a similar size model by Kato et al.
(1987). Akiyama et al. concluded: (1) The ultimate strength
of the SC structure was much higher than the corresponding
RC structure due to the significant contribution of the steel
plates; (2) cyclic loading causes some stiffness degradation
in the elastic range due to concrete cracking, and this degradation was about 30% for the SC structure as compared to
about 65% for the RC structure; and (3) the SC structure was
more ductile as the corresponding RC structure lost capacity
rapidly after peak load due to shear failure. It is important
to note that these conclusions were limited to specific SC
and RC structures that were tested by Akiyama et al. and
Kato et al., and the corresponding design, reinforcing and
connection details. These conclusions cannot be generalized, but they motivated extensive research and studies in
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Japan, China, South Korea, the United States and Europe to
establish rational design provisions, codes and standards for
SC structures.
Significant research on the behavior of SC walls for various loading conditions, both in-plane and out-of-plane, has
been performed in Japan (Takeuchi et al., 1998; Takeuchi et
al., 1999; Ozaki et al., 2000; Ozaki et al., 2001; Ozaki et al.,
2004; Mizuno et al., 2005), China (Song et al., 2014; Leng
et al., 2015a; Leng et al., 2015b), and South Korea (Moon
et al., 2007; Moon et al., 2008; Kim and Kim, 2008; Lee et
al., 2008; Lee et al., 2009; Hong et al., 2009). The research
in Japan and South Korea has been the basis for design standards for SC construction in Japan (JEAG, 2005) and South
Korea (KSSC, 2010), respectively.
In the United States, extensive research has been conducted over the past decade to evaluate the behavior of SC
walls and connections and to develop consensus design
standards, such as the AISC Specification for Safety-Related
Steel Structures for Nuclear Facilities including Supplement
No. 1 (AISC, 2015), hereafter referred to as ANSI/AISC
N690. For example,
• The behavior of SC walls subjected to accident thermal and mechanical loading was evaluated by Booth et
al. (2007), Varma et al. (2009), Varma et al. (2013), and
Booth et al. (2015a).
• The out-of-plane shear behavior and design of SC walls
was evaluated by Varma et al. (2011c), Sener and Varma
(2014), and Sener et al. (2016). The out-of-plane flexure
behavior of SC walls was analyzed by Sener et al. (2015a).
• The in-plane behavior and design of SC walls was evaluated by Varma et al. (2011e), Seo et al. (2016), and Kurt et
al. (2016a).
• The local buckling behavior of steel faceplates in SC walls
and the composite action between steel plates and concrete infill was evaluated by Varma et al. (2013), Zhang
(2014), Zhang et al. (2014), Zhang (2014), and Bhardwaj
and Varma (2016).
• The behavior and design of SC walls subjected to combined in-plane forces and out-of-plane flexure was presented by Varma et al. (2011b; 2014).
• The missile impact behavior and design of SC walls was
evaluated by Bruhl et al. (2015a; 2015b). The effects of
impulsive loading on the design of SC walls was also
evaluated by Bruhl and Varma (2015; 2016).
Fig. 1-1. Typical SC wall configuration (AISC, 2015).
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• The behavior and design of non-contact lap splices
between the steel plates of SC walls and rebar of RC components were evaluated by Varma et al. (2011d), and Seo
and Varma (2017). The direct shear strength of rebar coupler anchor systems for SC walls was evaluated by Kurt et
al. (2016b).
• The behavior, design and shear strength of SC wall-towall T-joints and corner or L-joints were evaluated by Seo
et al. (2013), Seo (2014), and Seo and Varma (2015).
• The design and detailing of faceplates, steel anchors and
ties of SC walls to prevent local buckling, interfacial shear
failure, and section delamination failure were presented
in Bhardwaj et al. (2017). This paper also presented the
design of steel anchors and ties to account for the effect of
combined shear forces.
• The lateral load capacity of SC walls with boundary elements was evaluated by Booth et al. (2015c). The lateral
load capacity of SC walls without boundary elements was
evaluated by Epackachi et al. (2015), Kurt et al. (2016a),
and Bhardwaj et al. (2015a).
SC walls are being increasingly used in nuclear facilities. GE Hitachi Nuclear Energy and Toshiba have used
SC walls for advanced boiling water reactor (ABWR)
Kashiwazaki-Kariwa Units 6 and 7 in Japan. These units were
opened in 1996 and 1997. Tokyo Electric Power Company
(TEPCO) used SC walls in ABWR Fukushima 7 and 8 units.
These units began commercial operation in 2007 and 2008.
Westinghouse Electric Corporation (WEC) has incorporated
SC modules for walls and floors of its AP1000 plant internal structures. A typical wall module panel for the AP1000
plant containment internal structure is shown in Figure 1-2.
Fig. 1-2. Typical structural wall module in AP1000 plant
(DCD, 2011) (©Westinghouse Electric Company, LC.
All rights reserved).
Figure 1-3 presents a preassembled internal structure SC
module. WEC also extended the use of SC modules to the
AP1000 shield building to make it resilient against aircraft
impact, a stipulated beyond design basis event. Construction
of several AP1000 units is under way in the United States
(South Carolina and Georgia) and China (Sanmen and Haiyang). Korea Hydro and Nuclear Power (KHNP) is incorporating SC construction in its advanced pressurized reactor
(APR+) standard plant. Mitsubishi Heavy Industries (MHI)
is doing the same for its advanced pressurized water reactor
(APWR) standard plant. The use of SC construction in small
modular reactors (SMR) is also currently being explored.
Commercial applications of SC wall piers—known as composite plate shear walls—with and without boundary elements, are also being considered in building construction.
1.2
ADVANTAGES OF SC WALLS
SC construction has numerous advantages over RC construction. The presence of faceplates in SC walls eliminates
the need for rebar and formwork. The use of faceplates facilitates fabrication of large empty modules in the shop. These
modules can then be shipped to the site and assembled in the
field. Figure 1-4 presents the comparison between modular
RC and SC construction. The schedule contraction achieved
by modular SC construction is illustrated in Figure 1-5.
Figure 1-6 presents fabrication, lifting and erection operations for some modules for AP1000 in China and the United
States (WEC-Sanmen Project and Vogtle Project). The figures illustrate the extent of schedule and modularity contraction achieved by SC construction.
Steel faceplates in SC walls provide better shielding
behavior. Compared to RC walls, the faceplates act as a barrier to incident radiation and reduce the intensity of radiation
passing through to the concrete infill. The improved performance enables up to a 10% reduction in wall thickness due
to reduction in the volume of concrete required for radiation
shielding. SC walls do not have problems associated with
rebar congestion or moisture loss due to evaporation. Faceplates in SC walls prevent moisture loss thus eliminating the
need for concrete curing. With proper use of concrete lifts,
the quality of placed concrete is generally superior to that
in RC construction. Existence of faceplates makes it easier
to incorporate major attachments, such as large bore pipe
supports during the initial construction. Additional minor
attachments can also be easily handled during the service
life of the structure. Similarly, the walls can be detailed during construction to accommodate any penetrations. The SC
walls have improved resistance to out-of-plane loads, such
as bending and shear, that may be due to seismic or accident thermal events. The faceplates also provide better leaktightness behavior, which reduces the loss of stored water.
The leak-tightness also protects the concrete during the service life of the structure.
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1.2.1
Resilience and Sustainability Aspects of
SC Construction
SC construction has natural benefits in terms of resilience and sustainability of the structure. The resilience performance of SC walls can be improved as
discussed in the following (Malushte and Varma,
2015).
(a) Missile and blast loads: The presence of faceplates leads to increased blast and missile resistance. This resistance is further improved by
higher strength faceplates with closer tie spacing.
(b) External hazard (environmental) or abnormal loads: SC construction typically results
in increased strength and ductility, leading to
higher margins against design basis external
hazard loads—for example, environmental hazards, such as seismic or tornado wind events.
This benefit is best realized if full-strength
connections—connections stronger than the wall capacities—are used to join SC elements with other connected
members, such as a basemat, and the reinforcement ratio
is kept between 0.02 and 0.04.
(c) Accident thermal loads: The accident thermal load,
resulting from a loss-of-coolant or main steam break
event, leads to exposure to elevated temperature for sustained duration. This loading poses a unique challenge
to SC members because the faceplate is immediately
exposed to the elevated temperature due to there being
no concrete cover. A seismic event could occur during
such extended exposure, which could be a beyond design
basis (BDB) consideration. Performance in these scenarios is improved by using full-strength connections, steel
or fiber reinforced concrete, or fire-resistant steel plates.
(d) Exposure to fire: The faceplate that is exposed to fire
loses strength and stiffness; however, similar to RC
construction, the bulk of the concrete and the opposite
Fig. 1-3. Example of large preassembled module in AP1000 plant (DCD, 2011)
(©Westinghouse Electric Company, LC. All rights reserved).
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faceplate maintain good strength and stiffness. As such,
SC structures have better fire resistance than pure steel
structures. Fire resistance of SC walls is potentially
lower than RC structures; however, the fire resistance is
enhanced if a suitable fire protection coating is applied to
the faceplate(s) or fire-resistant steel is used. The member strength and stiffness during fire exposure is also
improved by embedding another steel plate within the
concrete, that is, between the faceplates. ANSI/AISC
N690 does not currently cover SC walls with embedded
steel plates.
(a) Field labor force reduction: SC construction requires a
smaller field labor force compared to conventional RC
construction because of elimination of activities related
to formwork, rebar erection and curing. As in any modular construction, the degree of field labor reduction
depends on the extent of modularization and the size
of the modules. Use of automated welding techniques
can help further in this regard. Reduction in field labor
results in a significant reduction in the carbon footprint
associated with mobilization, demobilization, and daily
coordination between crafts.
(e) Durability and long service life: The faceplates improve
leak-tightness of concrete. However, just like any steel
structure, the exposed steel surfaces need to be protected
from corrosion. The protection scheme will depend on
the service environment; for example, interior versus
exterior walls and underground walls.
(b) Reduction of water usage: SC construction does not have
rebar congestion issues, therefore, the amount of water
used in the concrete mix design can be reduced without
sacrificing placement quality. Additionally, the water use
associated with concrete curing is eliminated.
Advantages and considerations of sustainability of SC structures include (Varma et al., 2015):
(c) Use of green concrete or cement substitutes: Cement is
an energy-intensive ingredient of concrete. Green concrete mixes—those replacing cementitious materials
(a) Modular SC Wall
(b) Modular RC Wall
Fig. 1-4. Typical modular SC and RC wall configurations (Schlaseman and Russell, 2004).
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with naturally occurring cement substitutes, such as fly
ash, pozzolan or slag—are always desirable from a sustainability standpoint. Unlike the schedule impact due to
the slow-setting pace of cement substitutes in RC construction, this issue is easily handled in SC construction
by ensuring that the faceplates are adequately designed
as permanent formwork.
(d) Prolonged service life: SC structures will have a long
service life provided the potential for steel plate corrosion is addressed. Depending on the application—underground wall, exterior wall exposed to atmosphere, or
walls exposed to water—certain types of stainless steel
can be used advantageously. Compared to surface treatment options, such as cathodic protection or surface
coatings, the stainless steel option may be the most cost
efficient in the long term.
(e) Surface decontamination: The ability to decontaminate
the exposed surfaces and the effort required to do so is
an important consideration in any nuclear facility. The
presence of faceplates provides an easy decontamination
process during the service life and after decommissioning. Faceplate surface treatment and material selection
can be especially important based on ease of decontamination. This is a sustainability consideration in terms of
controlling potential spread of radioactive materials.
(f) Potential for recycling: Unlike rebar in RC construction, the steel faceplates can be more easily removed and
recycled. Also, the concrete can be pulverized and used
in rubblized pavement construction.
(g) Reduced energy use during construction: SC construction has reduced the need for concrete compaction—
consolidation using vibrators—because there is no
congestion due to rebar. Self-consolidating concrete can
be used for hard to reach areas under penetrations. Additionally, options for field bolting can be maximized to
reduce energy consumption during construction.
(h) Material savings in steel and concrete quantity: Because
of higher strength and radiation shield capability, SC
member design can be optimized for a reduced amount
of steel and concrete versus comparable RC members.
This aspect has to be investigated during the design
phase. The quantity reductions have obvious sustainability implications.
(i) Elimination of water-stops and rebar accessories: Compared to conventional RC construction, SC construction
has a reduced need for water-stops—because of its inherent leaktightness—and accessories such as rebar chairs.
This results in a reduction of the rubber and plastic-based
materials, which is good in terms of sustainability.
Fig. 1-5. Schedule contraction by means of SC construction (Schlaseman and Russell, 2004).
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(a) Tie bar and stud layout
(©2009 Sanmen Nuclear Power Company Ltd.
All rights reserved)
(b) Panel section ready to be transported
(©2009 Sanmen Nuclear Power Company Ltd.
All rights reserved)
(c) Sub-module wall
(d) Welding of a sub-module
Fig. 1-6. Fabrication, lifting and erection operations for AP1000 modules in China and the United States.
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(e) Module inside the fabrication yard
(f) Module being transported (©2009 Sanmen Nuclear Power Company Ltd. All rights reserved)
Fig. 1-6. Fabrication, lifting and erection operations for AP1000 modules in China and the United States (continued).
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1.3
(j) Increased potential for modular attachment of supported
commodities: SC modules can be designed to further
enhance the ability to support or attach piping, equipment components and structural components, such as for
floors or platforms. The integrated SC module is assembled in the fabrication yard with these components. This
will lead to further reduction in the associated labor
forces and energy use on site, in addition to the resulting
schedule contraction.
LIMITATIONS OF SC WALLS
SC construction has some potential limitations in comparison with RC construction. SC walls have reinforcement—steel faceplates—exposed to the atmosphere. This
renders the reinforcement susceptible to corrosion in harsh
environments. Additionally, SC walls are expected to experience higher strength demands due to accident thermal
loads and fire events. Because the use of SC construction is
relatively new, there may be some fabrication and construction tolerance issues. Modular SC walls involve significant
(g) Module erected at site
(h) Lifting and erection of SC modules (©2009 Sanmen Nuclear Power Company Ltd. All rights reserved)
Fig. 1-6. Fabrication, lifting and erection operations for AP1000 modules in China and the United States (continued).
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prefabrication and specialized transportation, which may
sometimes lead to the labor and material cost of these SC
walls being higher than conventional RC construction. However, these limitations are addressed by choosing appropriate
materials and utilizing the best practices in fabrication and
construction.
1.4
ANSI/AISC N690 APPENDIX N9
Previously, the use of SC construction in the United States
had been hindered by the absence of a U.S.-based design
code for SC walls. However, in 2006 AISC formed a subcommittee on modular composite construction under the
Committee on Specifications Task Committee 12 for nuclear
structures. Over the next nine years, from 2006 to 2015, a
specification for the design of SC walls in safety-related
nuclear facilities was developed and finalized as an appendix (Appendix N9) to ANSI/AISC N690 (AISC, 2015). The
new appendix was incorporated into ANSI/AISC N690 as
Supplement No. 1. An outline of Appendix N9 and a brief
discussion of how the provisions of the appendix may be
used are provided in Bhardwaj et al. (2015b).
Appendix N9 is applicable to the design of SC walls and
their connections and anchorages. The experimental database that forms the basis of the provisions is discussed in
the commentary to Appendix N9. The appendix is limited
to SC walls with two faceplates on exterior surfaces and
no additional reinforcing bars. General requirements of the
appendix specify the conditions necessary for applicability
of the provisions. Detailing requirements of the appendix
address SC-specific limit states of local buckling, interfacial
shear failure, and section delamination. The appendix discusses the analysis procedures and presents the guidelines
for analysis. The demand types and available strengths for
individual demands are presented. The appendix also presents the interaction surfaces for combinations of demands.
Connection design philosophy, detailing for regions around
openings, design for impactive and impulsive loads, and
quality assurance checks are other topics addressed by the
supplement.
The Appendix is applicable to straight SC walls. If the
SC walls in application have any curvature, the effects of
curvature on detailing and design of the SC walls need to
be evaluated. This is necessary as there is limited data available for curved SC walls at present (Yan et al., 2015; Yan et
al., 2016). For the ratio of radius of curvature-to-thickness
values greater than 20, the effects of curvature may be negligible, and the provisions of Appendix N9 would be applicable. However, for the ratio of radius of curvature-to-section
thickness values less than 20, project-specific design and
detailing requirements for SC walls is warranted.
Alternate design methods for SC walls not meeting the
general provisions may be based on (1) project-specific
large-scale test data, or (2) results of nonlinear inelastic
analyses conducted using modeling approaches that are
benchmarked against applicable test data and peer reviewed.
Alternatively, subject to peer review, the wall design may
also be performed in accordance with ACI 349-06 (ACI,
2006) provided that (1) the faceplate thickness and its composite action is minimized to primarily enable it to function
as formwork; (2) conventional rebar is provided to develop
adequate section strength for demands due to in-plane and
out-of-plane forces and moments; and (3) the faceplates are
evaluated for stresses and strains due to strain compatibility
to ensure that they remain below the yield and local buckling
threshold, similar to the design of liner plates in concrete
containment structures according to ACI 359 (ACI, 2001).
(i) Lifting and erection of SC modules
(©WEC, LLC; ©Sanmen)
(j) Lifting and erection of SC modules
(©WEC, LLC; ©Sanmen)
Fig. 1-6. Fabrication, lifting and erection operations for AP1000 modules in China and the United States (continued).
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Chapter 2
Scope and Layout
This Guide is intended to facilitate the design of SC walls for
safety-related nuclear facilities. The procedures outlined in
this document are based on Supplement No. 1 to the AISC
Specification for Safety-Related Steel Structures for Nuclear
Facilities, ANSI/AISC N690 (AISC, 2015). Appendix N9,
adopted into ANSI/AISC N690 as part of the Supplement,
presents the requirements for the design of SC walls. Any
reference to Appendix N9 in this Design Guide is referring
to ANSI/AISC N690 Appendix N9. This Design Guide is
to be used in conjunction with ANSI/AISC N690. The
Design Guide:
• Addresses SC walls that meet the requirements of Appendix N9
• Provides supplementary recommendations for the
design of modular SC structures using the provisions of
Appendix N9
• Discusses the design of SC wall connections, including
design philosophies and typical connection details
• Presents illustrations explaining the tolerance requirements for construction and fabrication of SC walls
This Design Guide provides primary procedural steps
required for the design of SC structures. However, nuclear
construction needs to satisfy other regulatory and environmental requirements, which may affect the design procedure. There may be project-specific scenarios that need to
be considered in the design. The Design Guide may be used
as a platform for the design of modular SC walls for nuclear
construction.
This Design Guide discusses various aspects of the analysis and design of SC structures based on ANSI/AISC N690.
The minimum requirements that an SC wall needs to meet in
order for the provisions of Appendix N9 to be applicable are
discussed. This Design Guide then discusses the detailing
requirements for SC walls. These detailing requirements are
provided to address specific SC limit states, such as faceplate local buckling. The requirements include faceplate
slenderness requirements, and steel anchor and tie detailing.
Guidelines for modeling and analysis of SC walls are presented. Additionally, the determination and basis of individual design strength equations will be presented. Interaction
of demands is also discussed.
ANSI/AISC N690 provides procedural recommendations
for the design of SC wall connections. This Design Guide
addresses the design of connections in detail. Different connection philosophies, force transfer mechanisms, and types
of connections are discussed with illustrations. The implementation of the provisions of ANSI/AISC N690 Appendix
N9 is illustrated using a design example presented in Appendix A.
2.1
DESIGN EXAMPLE
This Design Guide provides a design example for an SC
wall structure. An SC wall from a compartment of a typical
safety-related nuclear facility is selected and all aspects of
the design of that wall are discussed. The design example is
presented in Appendix A. The example discusses the rationale for selecting the preliminary details of the structure.
Discussion of the basis for the material selection is presented
in the example. For brevity, the example does not present
the details of the finite element analysis models, procedures,
and results. Representative design demands are considered
for design of the SC wall. The SC wall considered does not
include any attachments or openings. The designed SC wall
is not checked for impactive and impulsive loading in the
example. It is considered that the fabrication and construction tolerances and quality assurance and control checks are
performed during the erection of the SC wall.
The design of modular SC walls needs to consider constructability aspects, such as fabrication and erection issues.
Based on transportation capabilities, the size of the prefabricated module is established. Specific analysis such as barge
transportation analysis may need to be performed for submodules, based on the erection and fabrication sequencing,
to consider the erection and fabrication loads, concrete casting pressure, and demands on ties and ribs prior to casting.
Therefore, the designers need to be cognizant of the fabrication and erection procedures and sequence to ensure the
design can be implemented without any issues. Appendix
N9 provides fabrication and erection tolerances that need to
be met for the provisions of Appendix A to be applicable.
These tolerances are discussed in Section 13 of this Design
Guide. While the design example presents the methodology
for the design of modular SC walls, the designer needs to
consider the constructability aspect of these walls during the
analysis and detailing phases of the design.
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Chapter 3
Minimum Requirements
The majority of SC wall tests have been performed on walls
with two faceplates, where composite action is provided
using either steel anchors or ties, or a combination of both.
The provisions of Appendix N9 in ANSI/AISC N690 have
been developed based on this experimental database and
the associated mechanics-based behavioral models. As a
result, Appendix N9 is limited to walls with two faceplates
anchored to the concrete infill by means of steel anchors or
ties, or a combination of both. The provisions are not applicable to SC walls reinforced with more than two steel plates,
which may be used for the design of the primary shield
structure supporting and shielding the reactor vessel. The
design of such structures composed of extremely thick SC
walls with three or more steel plates is discussed in Booth et
al. (2013, 2015b).
Appendix N9 is limited to the design of SC walls with
boundary elements or flanges, which are typically the purview of safety-related nuclear facilities consisting of labyrinthine SC walls connected to each other and to the concrete
floor or basemat. The modular composite specification does
not include provisions for the design of SC wall piers, with
no flanges or large boundary columns, that are typically
used in commercial building structures. The behavior and
seismic design of SC wall piers is discussed in Kurt et al.
(2016a), Epackachi et al. (2015), Bhardwaj et al. (2015a),
and the AISC Seismic Provisions for Structural Steel Buildings (AISC, 2016b).
Table 3-1 summarizes some of the minimum requirements for SC walls based on Appendix N9. These minimum
requirements were selected based on the range of parameters
in the experimental database of SC walls, and some other
criteria as described here. The minimum thickness, tsc, for
exterior walls is based on Table 1 of the Standard Review
Plan (SRP), Section 3.5.3, Revision 3 (NRC, 2007). The
maximum limit for tsc is based on the experimental database
of out-of-plane shear tests conducted on SC walls in Japan
(Ozaki et al., 2001), South Korea (Hong et al., 2009), and
the United States (Sener and Varma, 2014). The reinforcement ratio, ρ, is determined according to ANSI/AISC N690
Equation A-N9-1.
The limits for ρ, shown in Table 3-1, were established
because a very low reinforcement ratio—less than 0.015—
can lead to potential concerns regarding handling strength
and stiffness of empty modules and higher residual stresses
due to fabrication activities and concrete casting. The use
of very high reinforcement ratios—greater than 0.050—can
potentially result in higher concrete stresses and change the
governing in-plane shear limit state from steel faceplate
yielding to concrete compression strut failure, which can
potentially reduce the strength and ductility of SC walls.
The limits for faceplate thickness, shown in Table 3-1,
were established because a 0.25-in.-thick faceplate is needed
for adequate stiffness and strength during concrete placement and rigging and handling operations. Additionally,
faceplates thinner than 0.25 in. (6 mm) can have the material
properties and imperfections associated with sheet metal,
such as waviness, instead of structural plates (Bruhl and
Varma, 2016). The maximum faceplate thickness of 1.5 in.
(38 mm) corresponds to a reinforcement ratio of 0.050 for
a 60-in. (1500 m)-thick SC wall. The minimum thickness
for interior walls is based on the maximum reinforcement
ratio of 0.050 and minimum faceplate thickness, tp, equal to
0.25 in. (6 mm). The specified minimum values for interior
as well as exterior walls are conservatively slightly larger
than absolute minimum values.
A minimum yield stress of 50 ksi (350 MPa) is specified to prevent premature yielding of the steel faceplates
due to residual stresses from concrete casting and thermally
induced stresses from accident thermal scenarios, because
such premature yielding could limit the strength and ductility of SC walls (Zhang, 2014). High-strength steels with a
yield stress greater than 65 ksi (450 MPa) are typically less
ductile and, hence, not desirable for demands beyond the
design basis earthquake (Varma, 2000).
The use of concrete with a compressive strength less than
4 ksi (28 MPa) is rare in safety-related nuclear facilities,
with the possible exception of the concrete basemat. The
minimum concrete strength of 4 ksi (28 MPa) is also specified so that the minimum principal stress in concrete remains
in the elastic range while faceplate yielding occurs under
in-plane shear loading. The provisions of Appendix N9 are
based on test results of specimens with a specified minimum
concrete compressive strength of 8 ksi (55 MPa) or less. Figure 3-1 presents the range of concrete compressive strengths
from the experimental database for out-of-plane shear tests
conducted internationally and discussed in Sener and Varma
(2014). In Figure 3-1, the ordinate presents the ratio of the
experimental out-of-plane shear strength, Vexp , with respect
to the nominal out-of-plane shear strength calculated using
ACI 349-06 (ACI, 2006) code equations, Vn.ACI, as discussed
in Sener and Varma (2014). The entire experimental database of SC walls consists of specimens with concrete compressive strengths in the range of 4 to 8 ksi (28 to 55 MPa).
Appendix N9 requires that for regions with holes, the
effective rupture strength of the region needs to be greater
than the yield strength, ensuring that the section undergoes a gross yielding failure and not a net section rupture.
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Table 3-1. Minimum Requirements for SC walls
Parameter
Minimum Value
Maximum Value
Reinforcement ratio, ρ
0.015
0.050
Faceplate thickness, tp
0.25 in. (6 mm)
1.50 in. (38 mm)
SC section thickness, tsc—interior walls
12 in. (300 mm)
60 in. (1500 mm)
SC section thickness, tsc—exterior walls
18 in. (450 mm)
60 in. (1500 mm)
Steel minimum yield stress, Fy
50 ksi (350 MPa)
65 ksi (450 MPa)
Concrete minimum compressive strength, ƒ′c
4 ksi (28 MPa)
8 ksi (55 MPa)
Fig. 3-1. Range of concrete compressive strength from
experimental database (Sener and Varma, 2014).
The majority of the experimental investigations have been
performed on SC walls with faceplates that have the same
nominal thickness and yield strength. The lack of uniformity
between the yield strength of the two faceplates exacerbates
the potential for section delamination through the plain concrete. The requirements of Appendix N9, Section N9.1.5,
consider delamination due to 50% nonuniformity between
the faceplate yield strengths. However, Section N9.1.1 conservatively stipulates that the nominal yield strength and
faceplate thickness be identical for both faceplates.
Appendix N9 permits that steel rib sections may be
welded to the faceplates of SC walls to increase the stiffness and strength of the empty modules. This increased stiffness improves the behavior of the empty modules during
transportation, handling and erection. The ribs also improve
the resistance of the faceplates to hydrostatic pressure from
concrete casting. After concrete hardening, the ribs prevent
local buckling of the faceplates. Therefore, when used in SC
walls, these steel ribs should be welded to the faceplates to
fully develop the yield strength of their connected element.
As shown in Figure 3-2, the embedment of the steel ribs into
the concrete is limited to prevent the use of large depth steel
ribs that can alter the mechanics of the SC wall behavior and
to minimize the interference of ribs on the performance of
the other steel anchors. However, the contribution of steel
ribs is not considered for any design parameters, such as
composite action or available strengths.
Fig. 3-2. Embedment depth of steel ribs.
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Chapter 4
Faceplate Slenderness Requirement
Local buckling of steel faceplates is an important limit state
to be considered in the design of SC walls. When subjected
to compressive stresses, the steel faceplates of SC walls can
undergo local buckling between the steel anchors. This local
buckling behavior of steel faceplates has been investigated
experimentally by Akiyama and Sekimoto (1991), Usami et
al. (1995), Kanchi (1996), Choi and Han (2009), and Zhang
(2014). These experimental studies have evaluated the
effects of the plate slenderness ratio—defined as the steel
anchor spacing, s, divided by the faceplate thickness, tp, and
the yield stress, Fy—on local buckling of faceplates. Zhang
et al. (2014) have summarized these experimental studies,
and conducted additional numerical analyses to confirm and
expand the experimental database. Figure 4-1 shows the
relationship between the normalized critical buckling strain,
buckling strain/steel yield strain, εcr/ εy , and the normalized
faceplate slenderness ratio, s/ tp × Fy/E. As shown, εcr is reasonably consistent with Euler’s column buckling curve with
partially fixed (K = 0.7) end conditions. Additionally, no data
points are located in the shaded region, which implies that
yielding in compression occurs before local buckling for a
faceplate slenderness ratio, s/ tp, less than 1.0.
Based on this investigation, ANSI/AISC N690 limits
the slenderness ratio—the width-to-thickness ratio of
the faceplates—as given by ANSI/AISC N690 Equation
A-N9-2. Because ties may also act as steel anchors, ANSI/
AISC N690 Equation A-N9-2 considers the largest unsupported length between rows of steel anchors or ties, b. For
steel faceplates with a specified minimum yield stress greater
than or equal to 50 ksi (350 MPa), the specified slenderness limit of ANSI/AISC N690 Equation A-N9-2 implicitly
addresses the influence of residual stresses or stresses due to
concrete casting. The use of faceplates with a specified minimum yield stress less than 50 ksi (350 MPa) is not permitted
because the slenderness limit of ANSI/AISC N690 Equation A-N9-2 cannot assure yielding in compression before
local buckling due to the influence of residual stresses and
concrete casting stresses (Zhang, 2014).
Fig. 4-1. Relationship between buckling strain and normalized slenderness ratio, K = 0.7 (adapted from Zhang et al., 2014).
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Chapter 5
Steel Anchor Detailing
The steel faceplates are anchored to the concrete infill by
steel anchors and ties. These anchors prevent local buckling
of the steel faceplates as discussed in the previous section,
and develop composite action between the faceplates and
concrete infill by transferring interfacial shear forces and
restraining slip between them. Developing composite action
can be understood in terms of: (1) developing the strength
of the composite section without premature failure of the
anchors or (2) developing strain compatibility between the
steel and concrete components.
Steel limit state design emphasizes developing the
strength of the composite section. For example, consider the
design of composite steel beams in ANSI/AISC N690 Chapter NI, Section I3, where full composite action is defined by
the ability of the anchors to develop the strength of the composite section as governed by the yield strength of the steel
or concrete components. This full composite action, in terms
of strength, is accompanied with interfacial slip and lack of
strain compatibility between the steel and concrete components. Enforcing full composite action in terms of strain
compatibility between the steel and concrete components
can be onerous in terms of the required number and spacing of steel anchors, while providing little to no additional
strength over that achieved by developing full composite
action in terms of strength (Selden et al., 2015). However,
the corresponding lack of strain compatibility due to inter­
facial slip may lead to reduction in stiffness of the composite
section, which is usually calculated assuming strain compatibility (plane sections remain plane).
Steel anchors used in SC construction may consist of
steel headed studs, embedded steel shapes, ties (smooth or
deformed), or a combination thereof, which can be attached
to the faceplates by welding or bolting. The following subsections discuss (1) the classification of steel anchors as
ductile or nonductile, (2) the required spacing to develop
the yield strength of the steel faceplate, (3) the influence of
interfacial slip on the stiffness, and (4) the required spacing
of steel anchors to prevent interfacial shear failure from governing the behavior of SC walls.
5.1
CLASSIFICATION OF STEEL ANCHORS
Steel anchors that have a ductile shear force-slip behavior
can redistribute the interfacial shear equally over several
connectors. These connectors, such as steel headed stud
anchors, are referred to as yielding type. Steel anchors that
have a nonductile shear force-slip behavior cannot redistribute interfacial shear and are referred to as nonyielding type.
As shown in Figure 5-1, an interfacial slip capability of at
least 0.20 in. (5 mm) before reduction in shear strength to
90% of the available shear strength is required to qualify
a yielding-type connector. Steel headed stud anchors are
typically capable of sustaining at least 0.20 in. (5 mm) of
interfacial slip in a ductile manner (Ollgaard et al., 1971).
The available strength of steel headed stud anchors can be
obtained from the AISC Specification for Structural Steel
Buildings, hereafter referred to as the AISC Specification
(AISC, 2010b). All other types of steel anchors need to be
tested to determine their available shear strength and interfacial slip capability. An adequate number of tests must be
performed to ascertain the available strength of nonyielding
steel anchors. The safety factors applicable for nonyielding
steel anchors can be obtained from the experimental studies by following the reliability analysis procedures used by
Ravindra and Galambos (1978).
For cases where a combination of yielding and nonyielding steel anchors is used, the system is classified conservatively as nonyielding because the peak strengths of yielding
and nonyielding steel anchors may not occur at similar slip
displacement levels, and the post-peak behavior of yielding
and nonyielding steel anchors may be significantly different,
and as a result, the interfacial shear force cannot be distributed equally over several connectors. The system is classified as a nonyielding type, and the strength of yielding steel
anchors has to be limited to the strength corresponding to
the slip displacement at which the nonyielding steel anchors
reach their ultimate strength. This is illustrated in Figure 5-2.
5.2
SPACING OF STEEL ANCHORS
The spacing of steel anchors is controlled by one of the
following:
(a) The requirement to prevent the faceplate from buckling
before yielding in compression.
(b) The requirement to achieve a desired development
length.
(c) The requirement to prevent interfacial shear failure from
occurring before out-of-plane shear failure.
While item (a), the faceplate slenderness requirement, was
discussed in Section 4, the other two requirements are discussed in Sections 5.2.1 and 5.2.2.
5.2.1
Development Length
The steel anchors develop composite action between the steel
faceplate and the concrete infill. The development length, Ld,
is the distance over which the steel faceplate can develop
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its yield strength due to the shear strength and number of
steel anchors. Thus, any target development length can be
achieved by designing the size and spacing of steel anchors.
The target development length has a direct influence on the
degree of composite action, in terms of the strain compatibility achieved between the steel faceplate and concrete infill.
This partial composite action—strain compatibility or interfacial slip—has a direct influence on the flexural stiffness,
EI, of the composite section.
Zhang et al. (2014) investigated the relationship between
the target development length and the degree of composite
action (strain compatibility) between steel and concrete.
They concluded that the target development length should
not exceed three times the section (or wall) thickness, tsc,
and that 75 to 90% partial composite action (strain compatibility) can be achieved for target development lengths less
than or equal to 3tsc. They also investigated the relationship
between the partial composite action (strain compatibility)
and flexural section stiffness, EI, of the composite section.
They concluded that 75 to 90% partial composite action
(strain compatibility) does not have a significant influence
(less than 10%) on the cracked-transformed flexural stiffness, EI, of the composite section.
Based on Zhang et al. (2014), ANSI/AISC N690 Appendix N9 requires the development length to be less than or
equal to 3tsc. For the range of geometric parameters used
in nuclear construction—wall thickness tsc, plate thickness
tp, and stud anchor diameter and spacing—this requirement
(Ld ≤ 3tsc) will result in faceplate development lengths that
are comparable to ACI 349-06 (ACI, 2006) based development lengths calculated for No. 11, 14 or 18 rebar used typically in nuclear concrete construction.
Figure 5-3 shows the free-body diagram associated with
the development length, Ld, of the steel faceplate. In the diagram, the width of the faceplate is equal to the transverse
spacing of the stud anchors, sT, and the faceplate develops the yield stress, Fy, over the development length. For
designs with yielding stud anchors, the interfacial shear
force is assumed to redistribute uniformly over the development length, and the value is governed by the available
shear strength, Qcv, of the yielding anchor. Zhang et al.
(2014) developed Equation 5-1 using the free-body diagram
shown in Figure 5-3 to relate the development length, Ld, to
the available shear strength, Qcv, and the spacing of yielding
steel anchors:
Q cv
Ld
≥ sT t p Fy
sL
(5-1)
where
Fy = specified minimum yield stress, ksi (MPa)
L d = development length for faceplate, in. (mm)
sL = longitudinal spacing of steel anchors, in. (mm)
sT = transverse spacing of steel anchors, in. (mm)
tp = plate thickness, in. (mm)
Equation 5-2 was developed by the authors for nonyielding stud anchors. The interfacial shear force is assumed to
distribute linearly over the development length, and the maximum value is governed by the available shear strength, Qcv,
of the nonyielding anchor. Both Equations 5-3 and 5-4 are
based on the consideration that the total shear strength of the
anchors over the development length should be greater than
or equal to the yield strength of the faceplate:
Peak strength
Ry
90% Peak strength
Shear Force,Q, kips
0.9Ry
Conduct statistical evaluation of results
(peak strength, slip90%) from pushout tests to
establish:
1) Available shear strength, Qcv
2) Available slip90%
3) If available slip90% ≥ 0.2 in., then yielding
steel anchor
4) If available slip90% < 0.2 in., then
nonyielding steel anchor
Slip Displacement Δ, in.
slip90%
Fig. 5-1. Typical steel anchor force-slip behavior from
pushout tests (Bhardwaj et al., 2017).
Fig. 5-2. Strength of yielding steel anchors that form part of a
nonyielding steel anchor system (Bhardwaj et al., 2017).
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1
L
Qcv d ≥ sT t p Fy
2
sL
(5-2)
The stud anchor spacing, s, is typically equal in the longitudinal, sL, and transverse, sT, directions, and Equation 5-1
and 5-2 can be simplified to Equation A-N9-3 of Appendix N9. The engineer selects or designs the development
length, Ld, for the SC wall, and calculates the stud anchor
spacing required to achieve it. The development length cannot exceed three times the wall thickness.
5.2.2
Interfacial Shear
When subjected to an out-of-plane shear force, V, there
are three potential failure modes: (1) out-of-plane flexural
yielding, (2) out-of-plane shear failure through the concrete
infill and the ties, or (3) interfacial shear failure at the steelconcrete interface through the shear connectors. The outof-plane flexural yielding limit state is discussed in detail
by Sener et al. (2015b), and the out-of-plane shear failure
mode is discussed in detail by Sener and Varma (2014). They
have also provided available strength equations for SC walls.
Appendix N9 includes equations for calculating the available flexural strength, ϕb Mn or Mn/ Ωb, based on Sener et al.
(2015b), and the available out-of-plane shear strength, Vc , of
SC walls based on Sener and Varma (2014). Therefore, this
subsection focuses on the third failure mode—inter­facial
shear failure—which is somewhat similar to bond shear
failure in reinforced concrete beams. The design philosophy
is to prevent interfacial shear failure from occurring before
out-of-plane shear failure; that is, interfacial shear failure
should not be the governing failure mode of the three potential modes.
Figure 5-4(a) shows the free-body diagram of an SC wall
subjected to out-of-plane shear force. The out-of-plane shear
force, V, increases the out-of-plane bending moment, M, by ∆
along the length of the shear span, Lv. As a result, the tensile
force in the steel faceplate increases by Δ/ jtsc over the shear
span length, where jtsc is the arm length associated with the
bending moment over the cross section and can be estimated
conservatively as 0.9tsc (Sener et al., 2015b). This increase
in the tensile force is in equilibrium with the interfacial shear
flow between the steel faceplate and concrete infill, which is
resisted by the steel anchors as shown in Figure 5-4(b). The
interfacial shear strength of the anchors must be greater than
or equal to the shear flow demand to prevent failure.
Figure 5-4(c) shows the free-body diagram with yielding
anchors resisting the interfacial shear flow. The interfacial
shear strength is equal to the number of anchors—calculated
as the shear span length divided by the longitudinal spacing, Lv/sL—multiplied by the available shear strength, Qcv ,
of the yielding anchor. As expressed by Equation 5-3, the
interfacial shear strength should be greater than or equal to
the demand shear flow. If the longitudinal and transverse
spacing of anchors is equal, s = sL = sT, then Equation 5-3
can be simplified to Equation 5-4. In Equation 5-4, ∆/Lv is
equal to the out-of-plane shear force, V, and is limited to the
out-of-plane available shear strength, Vc , of the SC wall section. Thus, Equation 5-4 can be simplified to Appendix N9
Equation A-N9-4, which specifies the maximum spacing, s,
of anchors to prevent interfacial shear failure from occurring
before out-of-plane shear failure.
Similarly, Figure 5-4(d) shows the free-body diagram
with nonyielding anchors resisting the interfacial shear flow.
For this case, the interfacial shear strength is equal to onehalf of the number of anchors, calculated as Lv/ 2sL, multiplied by the available shear strength, Qcv , of the nonyielding
anchor, because the most stressed nonyielding anchor will
fail before redistributing the shear flow over several anchors.
Similar to the previous discussion, Equation A-N9-4 specifies the maximum spacing, s, of anchors to prevent interfacial shear failure from occurring before out-of-plane shear
failure of the SC section. In Equation A-N9-4, the factor c1
distinguishes between the design of yielding and nonyielding anchors.
Qcv
L v Δ Mx
≥
sT
sL 0.9tsc (5-3)
s≤
Qcv ( 0.9tsc )
Vc
(5-4)
sT
Faceplate
sL
Steel anchors
sT tp Fy
Fig. 5-3. Yielding steel anchor spacing requirement (Zhang et al., 2014).
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where
Lv = length of shear span, in. (mm)
Mx = nominal flexural strength per unit width, kip-ft/in.
(N-mm/m)
Vc = available out-of-plane shear strength per unit width
in SC wall section, kip/ft (N/mm)
s = steel anchor spacing, in. (mm)
tsc = SC section thickness, in. (mm)
The spacing of steel anchors needs to be the lesser of the
spacing determined from Equations A-N9-3 and A-N9-4.
Steel anchor spacing is typically governed by Equation
A-N9-3, which includes the requirement for the development length to be no greater than 3tsc. However, for portions
of the SC structure subjected to an extremely large out-ofplane moment gradient, Equation A-N9-4—the requirement
for interfacial shear strength to be greater than the available
out-of-plane shear strength—may control the steel anchor
spacing.
Vyz+ ΔVyz
My+ΔMy
Faceplate
Vxz
z
Mx
y
x
Mx+ΔMx
sT
Vxz+ ΔVxz
Crack
My
Lv
Vyz
Faceplate
Mx
× sT
0.9tsc
cv
×
v
sL
L
Steel anchors
M x + ΔM x
× sT
0.9tsc
Lv
(a) Forces on SC wall section
Qcv
(b) Forces on lower faceplate
Nonyielding
Yielding
Qcv
Qc
v ×L
d s
L
(c) Shear resistance of yielding steel anchors
Qcv
½Q
cv ×
Ld
sL
(d) Shear resistance of nonyielding steel anchors
Fig. 5-4. Steel anchor spacing requirement for preventing interfacial
shear failure before out-of-plane shear failure (Bhardwaj et al., 2017).
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Chapter 6
Tie Detailing
Ties are required by Appendix N9 to connect the steel faceplates of the SC wall through the concrete infill. A tie may be
a single structural element, such as a tie rod, or an assembly
of several structural elements, for example a tie with a gusset
plate at one or both ends. They provide direct connectivity
between the steel faceplates and, along with the stud anchors,
enable the SC wall section to behave as an integral unit.
SC walls for nuclear applications can be extremely thick,
up to 60 in. as permitted by Appendix N9, with relatively
thin (0.5- to 1.0-in.-thick) steel faceplates on the surfaces. If
the steel faceplates are not tied together, there is a potential
failure mode that consists of splitting or delamination of the
wall section along a plane parallel to the faceplates through
the concrete thickness. Such a failure mode has only been
observed in the force transfer region of an axially loaded
eccentric lap-splice connection (Seo et al., 2016), but not in
member tests.
Ties serve multiple purposes in SC walls. They provide
structural integrity in terms of resistance to delamination
or splitting failure of the wall section through the concrete
thickness. They provide out-of-plane shear reinforcement
and contribute to the out-of-plane shear strength depending
on their classification and spacing. Ties act in tandem with
steel anchors to contribute to the interfacial shear strength
of SC walls. Ties can also participate in the force transfer
mechanisms associated with SC wall connections, if they are
engaged appropriately. Additionally, the ties serve to maintain form—often supplemented by reinforcing ribs or additional formwork—before or during concrete casting.
6.1
CLASSIFICATION AND SPACING OF TIES
The design tensile strength of ties considers the limit states
of gross yielding, net section rupture, and failure of tie-tofaceplate connections. If the limit state of gross yielding
governs, the ties are considered as yielding; otherwise the
ties are considered as nonyielding. Due to the differences
between nominal and actual measured material properties,
there may be cases where components that appear to be governed nominally by yielding may, in reality, be controlled
by nonyielding limit states. Therefore, Appendix N9, Equation A-N9-5, specifies a minimum margin between the nominal strength calculated for yielding and nonyielding limit
states. These requirements ensure that for ties to be classified
as yielding, their nominal rupture strength, or the nominal
strength of associated connections, should be at least 1.25
times the nominal yield strength. The nominal strength of
the associated connection is calculated as the governing
nominal strength of the welded or bolted connection of the
tie to the faceplate. The classification of ties as yielding or
nonyielding also governs their contribution to the out-ofplane shear strength.
The maximum spacing requirement for ties is influenced
by the tie spacing requirement for compression members
in ACI 349-06, Section 7.10.5.2 (ACI, 2006), which specifies that the tie spacing for reinforced concrete compression
members is not to exceed 16 longitudinal bar diameters,
48 tie diameters, or the least dimension of the compression
member. Due to the fundamental differences between reinforced concrete columns and SC walls, Appendix N9, Section N9.1.5, requires the ties to have a spacing no greater
than the section thickness, tsc.
6.1.1
Transfer Length
The transfer length, LTR, is defined as the length required to
develop strain compatibility between the steel and concrete
portions of the composite section if only one of the portions
is loaded at the end. The concept of transfer length is similar to load introduction length—the length over which steel
anchors transfer longitudinal shear in composite sections—
discussed in Section I6 of the AISC Specification (AISC,
2010b). Zhang et al. (2014) have analytically investigated
transfer lengths for composite SC walls subjected to axial
loading on the concrete only at the ends. As shown in Figure 6-1, strain compatibility (steel strain/concrete strain) or
the percentage of composite action increases with distance
from the concrete-only loaded ends. The transfer lengths are
typically greater than or equal to 3tsc, for SC walls with reinforcement ratios of 0.015 to 0.050.
Zhang et al. (2014) show that SC walls designed with
steel anchor spacing, s, to satisfy the faceplate slenderness
requirement of Appendix N9, Equation A-N9-3, and to
achieve development lengths, Ld, less than or equal to 3tsc,
have transfer lengths, LTR, greater than or equal to 3tsc. It is
important to note that the development length, Ld, is associated with the shear strength of steel anchors and their ability
to develop the yield strength of the faceplate. The transfer
length, LTR, is associated with the relative stiffness (forceslip behavior) of the steel anchors and their ability to develop
strain compatibility between the faceplates and concrete
infill. The transfer lengths are longer than the development
lengths for typical SC wall designs.
The effects of having transfer lengths longer than the
development lengths are inconsequential. The design capacities or available strengths of SC walls depend on developing
the yield strength of the faceplates, not strain compatibility.
The effective stiffness of the composite section depends on
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Fig. 6-1. Development of strain compatibility with distance from member end (from Zhang et al., 2014).
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strain compatibility but is dominated by the effects of concrete cracking. The effects of having longer transfer lengths
and 75 to 90% composite action on effective stiffness are
marginal compared to the reduction due to concrete cracking
(Zhang et al., 2014).
The transfer length used in the tie strength and spacing
requirements discussed in the following sections is limited
to 3tsc. Smaller values are improbable, and larger values will
reduce the required tensile force, Freq, that the ties have to be
designed for. Thus, using LTR = 3tsc is conservative for the
calculation of the required tensile strength.
6.2
of a postulated splitting or delamination failure mode in the
connection and load transfer region of an SC wall.
There are two loading cases, where forces are applied to
only one of the two components—faceplates or concrete
infill—that can introduce an eccentric moment, Mo, in the
SC walls. This eccentric moment is resisted by the ties. The
required tensile strength of the ties to resist the eccentric
moment can be determined as follows.
Case 1 is when the load is applied to concrete only, and
the moment is resisted by the composite section. If the compressive forces are applied only to the concrete, they will
transfer into the composite section over the transfer length,
LTR. Figures 6-2 and 6-3 illustrate the forces in the composite section. Over this transfer length, there will be an eccentric moment, Mo, that has to be resisted by the cross section
without splitting. The resisting moment, MR, is depicted in
Figure 6-4.
Figure 6-2 considers a lateral section of the wall length
along the transfer length, LTR. The compressive force applied
to the concrete on the left transfers to the composite section over the transfer length on the right. In Figure 6-3, Ks
and Kc are the stiffnesses of steel and concrete, respectively.
Figure 6-3 establishes that there is an eccentric moment,
Mo, resulting from the significant thickness, tsc, of the wall,
and the fact that the force applied on the left-hand side and
REQUIRED TENSILE STRENGTH OF TIES
The required tensile strength for ties is based on a postulated
failure mode of section delamination or splitting through the
concrete thickness of the SC wall. As mentioned earlier, this
failure mode has not been observed in any SC wall member
or component tests. However, it is possible in the connection regions of SC walls where only one of the two components, faceplates or concrete infill, are directly loaded—for
example, in eccentric lap splice anchorage of SC walls to
the concrete basemat (Seo and Varma, 2017). This failure
mode is improbable but catastrophic and can be prevented
by appropriately designed ties. This section develops the
required tensile strength of ties to prevent the occurrence
P ⎛ Ks ⎞
⎜
⎟
2 ⎝ Ks + Kc ⎠
P
tsc
P ⎛ Kc ⎞
⎜
⎟
tsc ⎝ K s + K c ⎠
P
stl
LTR
P ⎛ Ks ⎞
⎜
⎟
2 ⎝ Ks + Kc ⎠
Fig. 6-2. Load applied to concrete only, resisted by composite section.
P ⎛ Ks ⎞
⎜
⎟
2 ⎝ Ks + Kc ⎠
P
tsc
tsc/4
O
P ⎛ Kc ⎞
⎜
⎟
tsc ⎝ K s + K c ⎠
LTR
O
Mo
Fig. 6-3. Eccentric moment, Mo, acting to split section.
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the resultant on the right-hand side are not collinear. The
moment, Mo, is determined as shown in Equation 6-1:
n −1
i n ⎞
MR = ∑ ( 2 ) ( 0.5 Atie) ⎛ σ req
( i ) ( stl ) +
⎝
⎠
n
i =1
n
) ( n ) ( stl )
(2 ) ( 0.25 Atie) ( σ req
P ⎛ K s ⎞ ⎛ tsc ⎞
t
= steel plate force ⎛ sc ⎞
Mo = ⎜
⎟
⎝
⎠
⎝
2 ⎝ K s + Kc ⎠ 4
4⎠
(6-2)
= ⎡⎢
⎣
(6-1)
(n − 1)(2n − 1) n ⎤
n
+ ⎥ stl Freq
6
2⎦
⎡1 ⎛ L ⎞ 2 1 ⎤
n
= ⎢ ⎜ TR ⎟ + ⎥ stl Freq
⎝
⎠
3
s
6
tl
⎢⎣
⎥⎦
where
Kc = stiffness of concrete
Ks = stiffness of steel
P = applied force, kips (N)
tsc = SC section thickness, in. (mm)
Figure 6-4 shows how the eccentric moment, Mo, is
resisted by the ties with area, Atie, acting along with the
concrete in compression. As shown, the strain diagram is
assumed to be linear, but the contribution of the concrete to
resist tensile stresses is conservatively neglected. The size of
the concrete compression block is also assumed to be very
small to simplify calculations, and the contribution of the
concrete compression block to the resisting moment, MR, is
also conservatively ignored. As shown by the plan view in
Figure 6-4, a region of the wall with dimensions LTR and stt
with contributing ties is considered. The resisting moment,
MR, is calculated as shown in Equation 6-2 by including the
contributions of all the ties in the wall region:
where
Atie = area of ties, in.2 (mm2)
n
Freq
= tie force required to resist the overturning moment,
kips (N)
n
= Atieσ req
LTR = length of wall, in. (mm)
n = number of ties in the transfer length region
stl = width of wall, in. (mm)
n
σ req
= tie stress, ksi (MPa)
The required tie tensile strength for each individual tie,
Freq, is estimated by setting MR equal to Mo, and is given
by Appendix N9, Equation A-N9-6. Based on the study by
Zhang et al. (2014), a transfer length value of 3tsc has been
used in the formulation of Appendix N9, Equation A-N9-6.
The second case that can give rise to eccentric moments
is when the tensile forces are applied only to the faceplates.
Fig. 6-4. Resisting moment, MR .
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In this case, the forces will transfer to the composite section
over the transfer length, LTR, until concrete cracking occurs.
Once beyond this transfer length, there will be an eccentric
moment, Mo, that has to be resisted by the cross section
without splitting. Additionally, there may be a case where
there is an imbalance in the forces in the thick SC cross section due to different actual areas and yield strengths of the
faceplates. For example, under in-plane shear loading, the
composite section typically develops the yield strength of
the section, which could imply slightly different yield forces
in the faceplates due to differences in the actual areas or
yield stresses (Appendix N9 requires the faceplates to have
the same nominal thickness and yield stress). The required
force, evaluated using Equation A-N9-6, is applicable for
these cases as well.
The required force, Freq, is a hypothetical demand that has
been posited to ensure the structural integrity of the SC wall
by avoiding the splitting failure of the section. It should not
be deducted from the available strength of the ties.
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Chapter 7
Modeling Parameters for Analysis
SC wall structures are modeled using elastic finite elements.
Other methods of analysis have been ruled out because the
finite element method is the only practically feasible method
for global analysis of continuum structures. These finite elements can be thick-shell finite elements—such as a thick
shell with consideration of transverse shear stiffness/deformation, incompatible modes, or output of eight stress resultants—or solid finite elements. Rigid regions at joints may
be modeled for consideration of out-of-plane shear results
in connection regions. Finer meshes are used around section penetrations larger than half the wall thickness. When
using shell elements to model the expanse of the SC walls,
it is recommended to use meshes consisting of at least four
to six elements along the short direction and six to eight elements along the long direction. These numbers are based
on recommendations in ASCE 4-98 (ASCE, 1998) and will
adequately capture local modes of vibration. Finite elements
larger than 2tsc are not recommended for the interior regions.
Finite elements larger than tsc are not recommended for
connection regions or regions around section penetrations.
These element size limits are recommended based on the
design strength equations, which are calculated on a per unit
width basis, that are deemed appropriate up to 2tsc × 2tsc;
that is, the equations do not apply to the whole wall. The
limit on the mesh size ensures that the analysis outputs are
sufficiently accurate.
Seismic analyses of safety-related nuclear facilities
are typically conducted using the multi-step approach in
ASCE 4-98: the first step being dynamic soil structure interaction (SSI) analyses, and the second step being the subsequent equivalent static or dynamic analyses of the structure
only, using response from the SSI analysis as input (Varma
et al., 2014). The viscous damping ratios for a safe shutdown earthquake (SSE) seismic analysis can be assumed to
not exceed 5%, and this is based on 1/10th scale tests of
the entire containment internal structure (CIS) consisting of
SC modules (Akiyama et al., 1989). However, for custom
designs for an operating basis earthquake (OBE) where instructure response spectra (ISRS) need to be generated, a
damping ratio of 5% is unconservative and lower ratios may
have to be used, for example, 2 to 3%. Additional dynamic
analysis may be needed to determine the response of structures to impactive or impulsive loads. This is characteristic
of the structural design of safety-related nuclear facilities
and comparable to ACI 349-06, Appendix F (ACI, 2006),
and also to ANSI/AISC N690, Section NB3.15.
Second-order analysis will generally be unnecessary for
the labyrinthine structures where SC walls will be used. The
thickness of SC walls in a nuclear application will generally
exceed 2 ft (0.6 m). The typical wall height-to-thickness
ratios will meet the requirements of ACI 318 and ACI 318M,
Section 10.10.1(b) (ACI, 2008). In the rare situation that the
ACI requirements are not satisfied, the structure will generally meet the limitations of AISC Specification Appendix 7,
Section 7.3, allowing a first-order analysis to be performed
with notional lateral loads in lieu of a second-order analysis. Second-order analysis by the direct analysis method is
limited to steel frame structures with linear beam or column
elements. It is not applicable to labyrinthine structures made
up of SC or RC walls.
7.1
LOADS AND LOAD COMBINATIONS
Loads acting on the structure are determined based on ANSI/
AISC N690 Chapter NB2. Load combinations consistent
with those provided in Chapter NB2 are used to conduct
analysis and calculate the design force demands. The load
combinations imply linear superposition of the required
strengths. Analysis is performed for operating thermal combinations, Condition A, and accident thermal combinations,
Condition B. Because the analysis is elastic, the thermal
demands are combined with demands due to mechanical
loads using appropriate load combinations. The load combinations for operating thermal and seismic do not consider
concrete cracking. However, concrete cracking is considered
in accident thermal and seismic. The concrete is considered
cracked for both mechanical and thermal loads, and thus the
demands due to these loads are linearly superimposed.
7.2
GEOMETRIC AND MATERIAL
PROPERTIES FOR ANALYSIS
An elastic finite element model of the composite SC section
is developed using a single material. As mentioned earlier,
this model is the basic model for dynamic SSI and subsequent analysis. The SSI analysis model is often coarsely
meshed and will have soil and foundation modeled. The subsequent analysis model for structural design has finer mesh
for more accurate stress calculations (ASCE, 1998). For this
single material elastic model, the following steps are followed to determine the material properties:
(a) Poisson’s ratio, thermal expansion coefficient, and thermal conductivity of the material are matched to those of
the concrete, as these parameters will govern the thermally induced displacements of the structure.
(b) The model section thickness and material elastic modulus is calibrated so that the effective stiffnesses of the
model match those of the physical SC wall section.
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(c) The material density is calibrated to match the mass of
the model with that of the physical section.
strain; c is the distance to the neutral axis; and strain compatibility between the extreme concrete fibers and the faceplates is assumed.
The depth of the neutral axis can be determined from
equilibrium of the forces shown in Figure 7-1, which gives
ANSI/AISC N690, Equation C-A-N9-1a. The corresponding flexural stiffness, (EI)cr-tr , per unit width can then be calculated as given in ANSI/AISC N690, Equation C-A-N9-3a.
However, Varma et al. (2011a) calibrated this equation to the
simpler form given in ANSI/AISC N690, Equation A-N98. Studies from Booth et al. (2007) and Varma et al. (2009;
2011a) have further shown that operating thermal loading
conditions produce linear thermal gradients, which develop
gradually over time. As a result, there is little to no additional concrete cracking due to operating thermal loading and the cracked-transformed section flexural stiffness
applies. However, accident thermal loading increases the
faceplate temperature rapidly, while the concrete temperature lags behind. In addition, a nonlinear temperature gradient develops through the composite cross section because of
the significantly lower thermal conductivity of concrete, and
this gradient results in cracking of the concrete due to its low
tensile stress, ƒ′t .
The flexural stiffness recommendation accounts for the
potential cracking of the concrete due to the accident thermal
gradient through the composite section. It considers temperature increases greater than 150°F (83°C) on the faceplates
that result in full through-section concrete cracking—that is,
the flexural stiffness will be equal to that of the steel, EsIs,
alone. For faceplate surface temperature change from 0°F
to 150°F (−18°C to 66°C), the cracked-transformed flexural
stiffness, EsIs + c2 EcIc, is linearly reduced until it equals the
steel section stiffness, EsIs, which is the minimum effective
(d) The material specific heat is calibrated to match that of
the concrete. This will allow transient heat transfer analysis to be accurately conducted using the elastic, single
material, finite element model.
7.3
STIFFNESS VALUES FOR THE MODEL
The effective stiffness values used in the linear elastic model
are determined for operating thermal and accident thermal
conditions. Because there is uncertainty in the stiffness
manifest during the thermal accident event, upper (operating
thermal) and lower bound (accident thermal) stiffness values
are both considered for the analysis. The stiffness values are
determined by considering the expected pre-accident and
post-accident cracking. The basis of these stiffness values is
discussed in the following.
7.3.1
Effective Flexural Stiffness
The effective flexural stiffness for analysis of SC walls is
determined according to ANSI/AISC N690, Equation A-N98. The equation is based on experimental studies by Booth
et al. (2007) and Varma et al. (2009, 2011a). The studies
indicate that the uncracked composite flexural stiffness is
generally not manifest in SC walls. This is due to effects
of locked-in shrinkage strains in the concrete core, partial
composite action of the section, and reduced bond parameter
due to discrete steel anchor locations.
The cracked transformed flexural stiffness of the SC wall
for a wide range of parameters can be expressed using the
stress, strain and force block in Figure 7-1, where n is the
concrete-to-steel modular ratio, Ec/Es; ec is the top plate
12
12/n
Esec
12t pEs ec
Es ec
c
⎛ t ⎞
Es ec ⎜ sc ⎟
⎝ c − 1⎠
6c
n
⎛ t ⎞
12t pEs ec ⎜ sc ⎟
⎝ c − 1⎠
Fig. 7-1. Flexural stiffness of cracked-transformed section of SC walls.
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flexural stiffness. The average of the maximum surface temperature increases, ΔTsavg, is calculated by taking the average of the maximum surface temperature increases on the
max
max
two faceplates, ΔTs1 and ΔTs2 , due to accident thermal
conditions.
7.3.2
Effective In-Plane Shear Stiffness
The in-plane shear behavior of SC walls without accident
loading is governed by the plane-stress behavior of the faceplates and orthotropic cracked behavior of the concrete infill.
Ozaki et al. (2004) and Varma et al. (2011e) have developed
a trilinear shear force-shear strain model for SC walls with
reinforcement ratios, ρ, from 0.015 to 0.050. According to
this mechanics based model (MBM), composite uncracked
behavior of the SC wall occurs when the in-plane shear
force is less than or equal to the cracking threshold, Scr. Figure 7-2 shows a plot of experimental versus calculated values of cracking strength by Varma et al. (2014). The cracking
strength, Scr , is calculated assuming the shrinkage strain, εsh ,
to be 0.063 fc′ Gc . The pre-cracking shear stiffness can be
estimated as the composite shear stiffness, GAs + Gc Ac . It is
important to understand that the composite action between
the faceplates and the concrete infill, facilitated through the
steel anchors and ties, is discrete and not perfect.
After cracking, the tangent stiffness is governed by the
cracked orthotropic behavior of concrete acting compositely
with faceplates that are in a state of plane stress. However,
under seismic loading, the cyclic behavior of SC walls is
sec
governed by secant stiffness, K xy
, not tangent stiffness. The
secant stiffness can be estimated as a function of the applied
shear force, Srxy. Figure 7-3 illustrates the variation of normalized secant stiffness with normalized in-plane shear-force
for different values of the strength-adjusted reinforcement
sec
ratio, ρ. The secant stiffness, K xy
, is normalized with respect
uncr
to the uncracked stiffness, K xy , and the applied shear force,
Srxy, is normalized with respect to the nominal in-plane shear
strength, Vni. It is observed in Figure 7-3 that the secant stiffness drops exponentially after the occurrence of cracking,
cr
and reaches the cracked stiffness, K xy
, asymptotically.
Considering this variation in the secant stiffness, Varma
et al. (2011a) developed a simple model for estimating the
secant stiffness of SC walls, as shown in Figure 7-4. The
equations for in-plane shear stiffness of SC walls are based
on this model. For in-plane shear force values, Srxy, less than
the cracking threshold, Scr , the effective secant stiffness,
sec
K xy
, is the uncracked stiffness of the section. For Srxy values greater than twice the cracking threshold, the effective
stiffness is the post-cracking shear stiffness. Between Scr and
2Scr , Srxy is determined by linear interpolation.
The use of stainless steel plates does not change the inplane shear stiffness and strength of SC walls. The concrete infill is still the major contributor to the in-plane shear
stiffness before and after cracking. The contribution of the
stainless steel faceplates can be accounted for appropriately by using the corresponding value of shear modulus.
Fig. 7-2. Experimental versus calculated values of cracking strength (Varma et al., 2014).
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Additionally, the in-plane shear strength from ANSI/AISC
N690, Equation A-N9-19, will be slightly conservative for
stainless steel plates due to its lower elastic modulus and
early onset of strain hardening.
The in-plane shear stiffness of SC walls after accident
thermal loading was evaluated experimentally by researchers in Japan (Ozaki et al., 2000). As discussed in Varma et
al. (2011a), nonlinear (parabolic) thermal gradients develop
through the concrete section due to the loading. This gradient
induces concrete cracking in two orthogonal directions due
to the expansion of faceplates and the low cracking threshold of the concrete. The accident thermal loading eliminates
the uncracked shear force-strain behavior. Thus, the in-plane
shear stiffness of SC walls after accident thermal loading
can be estimated as the post-cracking shear stiffness of the
composite section. These orthogonal cracks due to thermal
loading do not reduce the in-plane shear strength of SC wall
panels significantly.
Fig. 7-3. Variation of secant stiffness of SC walls (Varma et al., 2011a).
Fig. 7-4. A simple model for secant stiffness with no accidental thermal loading (Varma et al., 2011a).
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7.4
MODELING THE OPENINGS
Any openings in the SC walls need to be modeled according to Section N9.1.7 of ANSI/AISC N690. The load redistribution around an opening creates stress concentrations,
the severity of which depends on factors such as size of the
opening, presence or absence of sharp reentrant corners, and
type and magnitude of loading. Under severe loading, the
faceplate may yield at or near the reentrant corners. However, the area over which yielding occurs and the magnitude
of plastic strain remains below the fracture strain limit as
long as (1) good detailing practices are used, and (2) the
faceplate effective stress due to averaged demands over a
small region around the opening is below the yield stress
limit. This philosophy is the same as in ASME pressure vessel design (ASME, 2013).
In addition to the effect on demands, the presence of an
opening affects the available strength of the SC panel section. This happens in two ways: (1) the region in the vicinity
of the opening is not fully effective as an SC section due
to the free edge of steel and concrete at the opening location, unless special detailing is provided to achieve a fully
developed faceplate at the opening perimeter; see Section
N9.1.7 of ANSI/AISC N690; and (2) the sharp reentrant corners of openings will lead to stress concentrations and large
plastic strains in the faceplate. Good detailing practices such
as avoiding sharp reentrant corners and development of the
faceplate to help redistribute the demands to regions away
from the edges and corners of the opening are required to
avoid loss in panel section strength due to the opening.
The detailing requirements aim at reducing the stress concentration effects and, if desired, achieving a fully developed
edge at the opening perimeter. Absent a fully developed edge
at the opening perimeter, a fully effective SC panel section
will be manifested some distance away from the free edge.
The pertinent detailing requirement limits the distance from
the free edge to the fully effective SC panel section.
Available literature provides data on the effect of small
openings on the section strength. This presents the possibility that the effect of small openings can be accounted for by
using simple prescriptive rules such that the analytical model
need not include small openings. With this in mind, Appendix N9 classifies the openings as small or large based on
whether their largest dimension is greater than or less than
half the thickness of the wall. The limit of tsc/ 2 is considered
adequately small compared to the evaluation size, 2tsc, of
panel section for calculating average design strength. The
modeling, detailing and evaluation criteria to be followed for
the SC wall region in the vicinity of small openings and large
openings is discussed in the following section.
7.4.1
Design and Detailing Requirements Around
Small Openings
To help ensure good connection performance, fully developed edges are required for small openings located within
the connection region; however, this does not necessarily
negate the need for connection qualification.
Design and Detailing for Free Edge at Opening Perimeter
Experiments conducted by Japanese researchers (Ozaki et
al., 2004) indicate that the maximum decrease in SC panel
section strength due to penetrations with an undeveloped
edge is about 15 to 20%. Based on these test data, the effect
of small openings is considered by conservatively taking
a 25% reduction in the strength of the affected SC panel
section(s). In case one panel section encompasses the opening (Opening A in Figure 7-5), the strength of just that panel
Fig. 7-5. Reduction in strength due to presence of opening.
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section is reduced. In case the opening lies in more than one
panel section (Opening B in Figure 7-5), the strength of all
panel sections that partially include the opening are reduced
by 25%.
Openings with sharp reentrant corners can still be problematic for the faceplate. The available test data does not
clearly address the effect of sharp reentrant corners. Because
of these considerations, some provision for corner radii is
warranted to avoid the potential for fracture at the sharp corners. The data point for this is derived from AISC Design
Guide 2, Steel and Composite Beams with Web Openings
(Darwin, 1990). Figure 7-6 illustrates the radius required to
be provided at the reentrant corners. The coping radius, typically twice the thickness, has been limited to four times the
thickness to try and further smooth the stress distribution.
To help maintain structural integrity against any potential
for splitting, a detailing requirement has been provided for
locating the first tie within tsc/ 4 from the edge of the opening.
Design and Detailing for Fully Developed Edge at
Opening Perimeter
With a fully developed edge at the opening perimeter, the
SC panel sections in the vicinity of the opening will be fully
effective beginning at the opening edge. A fully developed
edge is achieved by providing a welded steel sleeve across
the opening. This sleeve has two flange plates welded at
its ends to help transfer the faceplate stresses to the sleeve.
Normal and tractive stresses at the edge of the faceplate are
thus transferred to the sleeve, which in turn transfers them
to the concrete infill because it is anchored into the concrete
using steel anchors. The sleeve and flange plate thickness
and yield stress are specified such that faceplate stresses can
be adequately transferred to the concrete.
Fig. 7-6. Radius of reentrant corners
(view of the SC panel section).
The detailing for the sleeve can be thought of as a cylinder spanning across the SC wall section with annular discs
welded at its two edges. The flange plate is extended a minimum distance of one times the SC wall thickness to provide
additional strength in the stress concentration region. As
described in the following, the faceplate is welded to either
just the flange plates, or both the flange plates and the sleeve
depending on the thickness of the flange plate:
· In the case that the thickness of the flange plate is less
than 1.25 times the faceplate thickness, then the faceplate
acts as a doubler/reinforcing plate that helps deliver the
concentrated stresses to the sleeve (see Figure 7-7).
· If the flange plate is thicker than 1.25 times the faceplate
thickness, it is deemed capable of taking care of the stress
concentration effects by itself. Hence, the faceplate need
only be welded to the flange plate, which meets up with
the sleeve (see Figure 7-8).
No reduction in SC panel section strength is considered
because of exercising either of the detailing requirements.
Furthermore, as in the case of an opening with a free edge,
the stress concentration around openings is alleviated by
avoiding sharp reentrant corners.
7.4.2
Design and Detailing Requirements Around
Large Openings
Compared to the requirements for small openings, a more
rigorous set of criteria is followed for large openings.
Design and Detailing for Free Edge at Opening Perimeter
When detailed as a free edge, the opening is required to be
modeled as larger than the physical opening. The composite behavior of a wall section develops fully only after the
development length is reached. The SC wall in the intervening region cannot attain its full strength and is, therefore,
ignored in the analytical model. The faceplate development
length, Ld, is typically no greater than 3tsc. Thus, considering
a development length of just one times tsc, the as-modeled
opening dimension will be two times the section thickness
more than the physical opening dimension, as seen in Figure 7-9. For example, under this free edge option, a 4-ft
(1.2 m)-diameter circular opening in a 4-ft (1.2 m)-thick
SC wall will have to be modeled as a 12-ft (3.6 m)-diameter
opening, which may severely increase the resulting analysis-based demands for the surrounding SC panel sections
This risks the possibility that they will be inadequate unless
thicker faceplates are used locally.
Because the region of stress concentration and partial
composite action has not been modeled, no reduction in
strength needs to be considered for the as-modeled SC wall.
As in the case of small openings, stress concentration effects
are minimized by providing corner radii at reentrant corners.
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To help maintain structural integrity against any potential
for splitting, a detailing requirement has been provided for
locating the first tie within tsc/ 4 from the edge of the opening.
Design and Detailing for Fully Developed Edge at
Opening Perimeter
The edge will be fully developed with the same detailing
requirements as for small openings. However, the demands
need to be obtained by modeling the physical opening.
7.4.3
Bank of Small Openings
The region affected by a concentrated bank of small openings needs to be considered as a large opening when the
clear distance between adjacent small openings is equal to
or smaller than:
(a) 2tsc for openings designed and detailed for the free edge
at the opening perimeter.
(b) tsc for openings designed and detailed for the fully developed edge at the opening perimeter.
The physical dimensions of the large opening are equal to
the distance between the outermost edges of the bank of
small openings.
7.5
ANALYSIS INVOLVING ACCIDENT
THERMAL LOADS
Analyses for load combinations involving accident thermal conditions (Condition B) needs to include heat transfer
analyses. Heat transfer analyses is conducted using the geometric and material properties for the linear elastic material,
to estimate the temperature histories and through-section
Fig. 7-7. Small circular opening—detailing illustration for fully developed edge with flange plate thickness < 1.25tp .
Fig. 7-8. Small circular opening—detailing illustration for fully developed edge with flange plate thickness ≥ 1.25tp .
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temperature profiles produced by the thermal accident conditions. The heat transfer analysis results are used to define
thermal loading for the structural analyses.
Booth et al. (2007) and Varma et al. (2009) performed
experimental and analytical studies to evaluate the effect
of thermal loads—operating and accident—on the behavior
of SC walls. It was concluded that operating thermal stiffness of the composite walls can be predicted using cracked
transformed section properties. Upon applying accidental
thermal loads, a nonlinear thermal gradient develops across
the concrete cross section, causing the concrete to crack in
tension, as can be seen in Figure 7-10.
Figure 7-10 compares the experimental temperatures and
thermal gradients with those obtained from a fiber model.
This fiber model was then used to predict the momentcurvature, M-ϕ, response of the SC walls for the design
thermal loading. Figure 7-11 presents the M-ϕ responses
predicted for the specimen. The figure shows that the thermal gradient shifts the diagram to the left with nonzero
thermal curvature, ϕth , at zero moment and nonzero thermal
moment, Mth , at zero curvature. Figure 7-12 also shows that
the thermal moment can be related to the thermal curvature
using the fully cracked section stiffness.
The stiffness of the SC wall subjected to ΔTsavg greater
than or equal to 150°F (83°C) can be predicted using fully
cracked, steel only section properties. Based on the discussed
results, Varma et al. (2009) developed the equations given in
ANSI/AISC N690 to predict the effects of combined thermal
and mechanical loading in locations away from supports.
These equations do not apply at supports that may be fully
restrained from expansion. Temperature dependent properties for steel are not required for temperatures up to 400°F
Fig. 7-9. Modeling of large openings with free edge at opening perimeter.
(a) Analytically determined
(b) Experimentally determined
Fig. 7-10. Comparison of analytically and experimentally determined thermal gradients (Varma et al., 2009).
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(204°C). For temperatures greater than 400°F (204°C),
temperature dependent properties from ANSI/AISC N690
Appendix N4 are recommended.
7.6
INTERIOR AND CONNECTION REGIONS
Labyrinthine SC walls of safety-related nuclear facilities are
connected to each other and anchored to the concrete basemat. SC wall structures are connected to adjoining structures with the following connection types: SC wall-to-SC or
-RC wall, SC wall-to-basemat, SC wall-to-SC or -RC slab,
or splices between coplanar RC or SC walls. A connection
may be defined as the assembly of steel connectors, including steel headed stud anchors, anchor rods, ties, reinforcing
bars and dowels, post-tensioning bars, shear lugs, embedded
steel shapes, welds and bolts, rebar mechanical couplers,
and direct bearing in compression, and the surrounding
Fig. 7-11. Comparison of fiber model moment
curvature to transformed cracked and fully cracked
moment of inertia (Varma et al., 2009).
concrete materials anchoring the rebar or providing bearing
resistance that participate in the force transfer mechanisms
for tension, compression, in-plane shear, out-of-plane shear,
and out-of-plane flexure between two connected parts. It
does not include any portions of the SC walls being connected. The connection region is specifically designed to
undergo ductile yielding and energy dissipation during overloads. Force transfer from the composite SC wall to the supports or connected structures occurs within these connection
regions. Additionally, the connection regions serve as transition regions wherein the faceplates and concrete infill of SC
walls redistribute forces according to their relative stiffness
and develop composite action.
According to ANSI/AISC N690 Section N9.2, SC walls
are divided into interior regions and connection regions for
design purposes. Connection regions consist of perimeter
strips with a width not less than the section thickness, tsc, and
not more than twice the section thickness, 2tsc. Figure 7-13
illustrates the typical interior and connection regions for SC
walls. The requirement for connection regions to be less
Fig. 7-12. Relationship between moment and thermal gradient.
Fig. 7-13. The expanse of SC walls separated into connection regions and interior regions.
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than or equal to twice the wall thickness (≤ 2tsc) is based on
typical development lengths of No. 11 to No. 18 reinforcing
bars, which are used typically in nuclear construction. Specifying connection region lengths less than the wall thickness
(≤ tsc) can be impractical and lead to detrimental congestion
of steel anchors and ties.
7.7
REQUIRED STRENGTH DETERMINATION
Averaging and design assessment for interior regions is done
over 2tsc × 2tsc panel sections because the resulting section
demands account for a reasonable degree of yielding and
force redistribution at stress concentrations—for example,
first onset of significant inelastic deformation at SSE. While
the development length, Ld , is typically three times the section thickness, 3tsc, a lower value for averaging has been
used because 3tsc is deemed to be large considering typical SC wall thicknesses, such as for a 4-ft (1.2 m)-thick SC
wall. Keeping panel section dimensions at 3tsc would result
in 12-ft × 12-ft (3.6 m × 3.6 m) panel sections. This size
may result in very few panel sections per wall leading to less
accurate determination of demands for the SC walls. Averaging in connection regions and regions around openings has
also been limited to tsc , compared to the Ld value of 2tsc , for
the same reasons. Additionally, 3tsc is a notional value for
the development length. In most cases, the faceplates of SC
walls will be directly welded to steel base plates or other
faceplates, which will develop them immediately at the weld
location itself. Developing the faceplate yield strength over
the panel sections would not be an issue in most cases. The
sizing recommendations for panel sections are illustrated in
Figure 7-14.
The required strengths for the panel sections of SC walls
for each demand type is denoted as follows:
Mrx = required out-of-plane flexural strength per unit
width in direction x, kip-in./ft (N-mm/m)
Mry = required out-of-plane flexural strength per unit
width in direction y, kip-in./ft (N-mm/m)
Mrxy = required twisting moment strength per unit width,
kip-in./ft (N-mm/m)
Srx = required membrane axial strength per unit width
in direction x, kip/ft (N/m)
Sry = required membrane axial strength per unit width
in direction y, kip/ft (N/m)
Srxy = required membrane in-plane shear strength per
unit width, kip/ft (N/m)
Vrx = required out-of-plane shear strength per unit width
along edge parallel to direction y, kip/ft (N/m)
Vry = required out-of-plane shear strength per unit width
along edge parallel to direction x, kip/ft (N/m)
x, y = local coordinate axes in the plane of the wall associated with the finite element model
These demand types are shown in Figures 5-4a (out-ofplane shears and moments) and 9-2 (in-plane forces and
moments).
Fig. 7-14. Panel section sizing for averaging the design demands.
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Chapter 8
Individual Design Available Strengths
The available strengths of the SC wall section for individual demand types are determined based on ANSI/AISC
N690, Section N9.3. The concrete contribution to the tensile
strength of the section is not considered. Neglecting concrete
tensile strength is appropriate for SC sections because they
experience a higher degree of cracking due to curing shrinkage than typically observed in reinforced concrete sections.
This is due to locked-in tensile stresses in the SC concrete
core that result from restraint of curing shrinkage by the
faceplates, and also the discrete nature of the bond between
the reinforcing steel and the concrete core. The steel ribs
are provided primarily to increase faceplate stiffness and
strength to handle rigging and construction loads, such as
wet concrete pressure. Therefore, the contribution of the
steel ribs to available strength is neglected.
8.1
UNIAXIAL TENSILE STRENGTH
The tensile strength of the SC wall panel section is determined according to AISC Specification Chapter D. The
reduction in available tensile strength of the SC panel sections due to holes in faceplates is alleviated by avoiding tensile rupture in the faceplates.
8.2
COMPRESSIVE STRENGTH
The compressive strength of the SC wall panel sections is
determined according to ANSI/AISC N690, Equation A-N915. This equation is based on AISC Specification Section
I2.1b, with faceplates replacing the steel shape. The variables
that need to be redefined are discussed in ANSI/AISC N690,
Section N9.3.2. The SC wall panel sections are designed by
calculating the available axial compressive strength on a perfoot basis. The calculation uses the clear length of the wall
along the direction of loading and an effective SC stiffness
per unit width for buckling evaluation, which is based on
EIeff of the filled composite columns in AISC Specification
Chapter I. The equation for EIeff for filled composite columns has been simplified conservatively to EsIs+0.60EcIc.
The more accurate equation in AISC Specification Chapter I,
which is a function of the reinforcement ratio, can also be
used. Additionally, the effective length factor, K, has been
conservatively taken as 1.0.
ANSI/AISC N690, Equation A-N9-15 gives the nominal compressive strength for SC wall panel sections with
nonslender faceplates at operating temperatures. Varma
et al. (2013) used benchmarked finite element models to
Fig. 8-1. Load displacement curves: temperature magnitude as parameter (Varma et al., 2013).
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analytically study the impact of elevated temperatures on the
compressive strength of an SC wall.
Figure 8-1 shows the analysis results for different temperature magnitudes as well as faceplate slenderness ratios, s/tp.
The compressive strength of the analytical models has been
normalized with respect to the design strength calculated
using ANSI/AISC N690, Equation A-N9-15. The equation
becomes slightly unconservative for temperatures above
482°F (250°C). The figure also indicates that the duration of
heating does not affect the compressive strength of SC walls.
Therefore, ANSI/AISC N690, Equation A-N9-15 is recommended for calculating the compressive strength of SC wall
panel sections subjected to accident thermal loading causing
surface temperatures up to 300oF (149oC).
8.3
OUT-OF-PLANE FLEXURAL STRENGTH
The flexural strength of the SC wall panels is determined for
the limit state of faceplate yielding according to ANSI/AISC
N690, Equation A-N9-18. The equation is based on the consideration that the majority of the concrete infill depth will
be cracked in tension. The nominal flexural strength can also
be calculated using the reinforced concrete principles mentioned in ACI 349-06, Section 10.2 (ACI, 2006). The design
assumptions and limitations for determining available flexural strength of concrete members listed in the section can be
applied to SC walls with slight modifications accounting for
the differences from a RC design; in particular, having the
faceplates on the exterior faces (Sener et al., 2015b).
SC design is inherently similar to that of doubly reinforced concrete beams. Therefore, the concrete will not fully
crush (ε = 0.003) before the faceplate yields in compression
(ε = 0.002). In this case, the neutral axis will be located at
the inner surface of the faceplate. This limits the strain in
Fig. 8-2. Comparison of experimental flexural strength data
with strength obtained using modified ANSI/AISC N690
Equation C-A-N9-11 (Sener et al., 2015b).
the extreme fiber of the concrete in compression to the steel
yield strain. Concrete stress variation can be assumed to be
approximately linear up to the strain equal to the yield strain
of typically used faceplates (about 2,000µ). Assuming a triangular stress variation in concrete below this strain level
and transforming the compression faceplate to an equivalent
concrete block, Mn can be calculated by summing moments
about the centroid of the transformed block. Note that the
stress in the transformed concrete block is assumed equal to
the smaller of ƒ′c or Fy /n.
Sener et al. (2015b) compared the nominal flexural
strength values, Mn , obtained using the ANSI/AISC N690
Appendix N9 Commentary methodology (Equation C-AN9-11) with flexural strength data obtained from experimental studies by Japanese (Ozaki et al., 2001), South Korean
(Hong et al., 2009) and United States (Varma et al., 2011c)
researchers. Figure 8-2 plots the experimental out-of-plane
strength data normalized with Mn obtained as discussed previously. As shown, the flexural strength equation conservatively estimates the majority of the specimen capacities. It
is observed that there is no clear trend between the flexural
strength and section depth.
8.4
IN-PLANE SHEAR STRENGTH
The in-plane shear strength of SC wall panel sections is
determined according to ANSI/AISC N690, Equation
A-N9-19. In-plane shear behavior of the SC walls is governed by the plane stress behavior of the faceplates and the
orthotropic elastic behavior of concrete cracked in principal
tension. Ozaki et al. (2004) and Varma et al. (2011e) developed the fundamental in-plane behavior, mechanics based
model (MBM) for SC walls. The in-plane shear strength of
SC walls can be estimated as the trilinear shear force-strain
curve shown in Figure 8-3. The slope of the first part of the
curve is the in-plane shear stiffness prior to concrete crackuncr
ing, K xy
. The slope of the second part is the in-plane shear
cr
stiffness after the concrete cracking, K xy
, but before the faceplate yields. The third part of the curve corresponds to the
onset of faceplate Von Mises yielding. The expression for
shear yield strength, Vni, corresponding to the onset of yield
was calibrated to the simplified ANSI/AISC N690, Equation
A-N9-19. The calibration is for values of ρ between 0.01 and
0.04 for nuclear structures, where ρ is the strength-adjusted
reinforcement ratio calculated according to ANSI/AISC
N690, Equation A-N9-13. Thus, the in-plane shear behavior
is a function of ρ. Varma et al. (2014) compared the in-plane
shear strength of the specimen predicted by the MBM with
the experimental results. Figure 8-4 shows that the calculated and experimental values match closely, with the calculated MBM values being conservative.
Seo et al. (2016) verified the MBM using a large in-plane
shear test experimental database. The experimental in-plane
shear strength based on faceplate yielding was compared
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with design equations from ACI 349-06, the MBM, and
ANSI/AISC N690. The comparisons are presented in Figure 8-5. The ACI 349-06, Section 11, equation predicts the
in-plane shear strength slightly unconservatively; however,
the predication improves for higher reinforcement ratios.
The ANSI/AISC N690 in-plane strength equations predict
the in-plane shear strength conservatively.
8.5
OUT-OF-PLANE SHEAR STRENGTH
The out-of-plane shear behavior of SC walls is similar to
that of RC walls with some differences associated with
crack spacing and width due to the more discrete nature of
the bond—via steel anchors—in SC walls. Japanese (Ozaki
et al., 2001), South Korean (Hong et al., 2009), and U.S.
(Varma et al., 2011c) researchers have performed experiments to study the out-of-plane behavior of SC sections.
Sener and Varma (2014) have compared the shear strengths
obtained from this experimental database with the ACI
349-06 shear strength equations. The comparisons demonstrated that out-of-plane shear failure is a nonductile failure mode, and the concrete contribution to the out-of-plane
shear strength reduces with increasing wall thickness due
to size effects. Based on these observations, ANSI/AISC
N690 requires the nominal out-of-plane shear strength to be
established by conducting project-specific, large-scale, outof-plane shear tests; by using applicable test results; or by
using the provisions of ANSI/AISC N690, Section N9.3.5.
This section addresses the nonductile out-of-plane shear failure by defining suitable values for the resistance factor (ϕvo =
0.75) and safety factor (Ωvo = 2.00) based on the reliability
analysis presented in Sener and Varma (2014). The nominal
shear strength of the SC walls depends on the spacing of
shear reinforcement and the classification of shear reinforcement: yielding or nonyielding.
If the shear reinforcement is spaced less than tsc/ 2, the
nominal out-of-plane shear strength will include out-of-plane
shear contributions from concrete as well as from the steel,
with the ties acting as shear reinforcement. ANSI/AISC N690
Fig. 8-3. In-plane shear strain curve (Varma et al., 2011e).
• Experimental values
— Calculated values
Fig. 8-4. Experimental versus calculated values of in-plane shear strength (Varma et al., 2014).
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(a)
(b)
(c)
Fig. 8-5. In-plane shear strength of SC walls normalized with (a) ACI 349-06 equation,
(b) MBM equation, and (c) ANSI/AISC N690 equation (Seo et al., 2016).
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requires the out-of-plane shear strength for an SC wall with
shear reinforcement spaced not greater than half the section
thickness be determined by Equations A-N9-20 to A-N9-22.
ANSI/AISC N690, Equation A-N9-21, addresses the size
effect by limiting the out-of-plane shear contribution of the
concrete in SC walls to 0.05 fc′ (ksi) ⎡⎣1.5 fc′ (psi) ⎤⎦. The
shear reinforcement contribution is based on the well-known
mechanism of a shear or flexure-shear crack passing through
several yielding-type shear reinforcement ties and engaging
them in axial tension. The classification of the shear reinforcement, or ties, as yielding and the determination of the available axial tensile strength are important for this calculation.
ANSI/AISC N690, Equation A-N9-22, limits the maximum
possible contribution of shear reinforcement to out-of-plane
shear strength to 0.25 fc′Ac (ksi) ⎡⎣8 fc′Ac (psi) ⎤⎦ , where Ac is
the area of concrete per unit width. This upper limit is based
on ACI 349-06.
For nonyielding tie shear reinforcement, spaced no
greater than tsc/ 2, it is possible that the concrete shear or
flexure-shear crack will activate all the individual shear reinforcements that it will pass through. However, it is unclear
whether these individual shear reinforcements will be able
to develop their individual design strengths before one of
them—the one with the largest axial force—fails in a nonductile manner. Therefore, the shear reinforcement contribution given in ANSI/AISC N690, Equation A-N9-22, has
been reduced to one-half.
If the spacing of the yielding shear reinforcement is
greater than one-half of the section thickness, the maximum
out-of-plane shear strength is limited to the greater of the
concrete shear strength contribution, or the shear reinforcement contribution alone. This is based on the ability of the
SC section to develop an internal truss mechanism for equilibrium. The strength of this truss mechanism is limited to
that of the tie shear reinforcement. The concrete and steel
contributions cannot be added for shear reinforcement spacing greater than tsc/ 2 because the shear or flexural-shear
crack may not pass through more than one tie.
ANSI/AISC N690 Appendix N9 requires that the out-ofplane shear strength for an SC wall with shear reinforcement
spaced greater than half the section thickness needs to be the
greater of Vconc (ANSI/AISC N690, Equation A-N9-21) and
Vs (ANSI/AISC N690, Equation A-N9-22). The behavior of
nonyielding and yielding shear reinforcement with spacing
greater than half the wall thickness will be the same.
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Chapter 9
Interaction of Design Available Strengths
The interaction of design demands needs to be checked for
all load combinations. ANSI/AISC N690, Section N9.3.6
defines the limiting interaction of demands for SC walls.
9.1
INTERACTION OF OUT-OF-PLANE
SHEAR FORCES
The out-of-plane shear demands in both the x, or Vrx, and
y, or Vry, directions rely on using the same ties for the steel
contribution, Vs. Both Vrx and Vry subject the steel shear
reinforcement to axial tensile demand after the concrete
cracks and the concrete shear strength contribution, Vconc, in
respective directions is exceeded. Additionally, shear reinforcement and steel anchors are subject to interfacial shear
demands in both the x and y directions, where x and y are the
local coordinate axes in the plane of the wall, as shown in
Figure 5-4(a). An equation was developed to check the interaction of out-of-plane shear and interfacial shear demands
on an SC wall.
If the required out-of-plane shear strength per unit width
for both the x and y axes, Vrx and Vry, is greater than the
available out-of-plane shear strength provided by the concrete per unit width of the SC panel section, Vc conc, and the
out-of-plane shear reinforcement is spaced no greater than
half the section thickness, the interaction of out-of-plane
shear forces is limited by ANSI/AISC N690, Equation
A-N9-23. The interaction equation is based on the sheartension interaction equation in ACI 349-06, Appendix D,
Commentary RD.7 (ACI, 2006), which is applicable to connectors with ductile and nonductile limit states. In the first
part of the interaction equation, the numerators are the tensile force demands in the ties, which are calculated as the
portions of the out-of-plane shear demands greater than the
corresponding concrete contribution, Vconc. The denominators are the available strength contributions of the ties, Vs.
The second term in the interaction equation accounts for
the shear demand in the ties and steel anchors due to the
participation in resisting interfacial shear demands, which
are the result of out-of-plane shear demands as discussed
previously. The numerator is the vector sum of the out-ofplane shear demands, Vrx and Vry, obtained by mathematical
manipulation of ANSI/AISC N690, Equation A-N9-4. The
denominator is the weighted average of the shear strength
avg, and can be calcontributions of ties and steel anchors, Qcv
culated according to Equation 9-1.
avg
Qcv
=
tie
net Qcv
+ nesQcv
net + nes
(9-1)
where
tie
Qcv
= available interfacial shear strength of tie, kip (N)
nes = effective number of shear connectors contributing
to a unit cell
net = effective number of ties contributing to a unit cell
(the unit cell is the quadrilateral region defined by
a grid of four adjacent ties)
The unit cell is illustrated in Figure 9-1 for an SC wall
of thickness 36 in. (900 mm), with ties spaced at 36 in.
(900 mm) and steel anchors spaced at 9 in. (225 mm). As
shown in the figure, the ties at the corners participate in four
adjoining unit cells, and the steel anchors at the boundaries participate in two adjacent unit cells. The steel anchors
within the boundaries of the unit cells contribute fully. The
contribution of shear anchors needs to be modified in case
the anchors are nonyielding. For the example shown in
Figure 9-1, the effective number of ties contributing to the
unit cell, net , is equal to 1, and the effective number of steel
anchors, nes, is equal to 15 (1)(9) + (0.5)(12) = 15 .
When the spacing of the shear reinforcement is greater
than half the section thickness, the nominal out-of-plane
shear strength is governed by the greater of the steel or concrete contributions, as discussed previously. When the steel
contribution is greater than the concrete contribution, ANSI/
AISC N690, Equation A-N9-23, will not contain a concrete
contribution.
When one of the out-of-plane shear demands, Vcx or Vcy , is
less than the concrete contribution, there will be no interaction of out-of-plane shear demands. For shear reinforcement
spaced at greater than half of the section thickness, and if the
concrete contribution is more than the shear reinforcement
contribution, the concrete infill will be subject to two-way
punching shear—or one-way shear, depending on the wall
configuration—which will be resisted by the perimeter of
the unit cell for the SC panel section.
[
9.2
]
IN-PLANE FORCES AND OUT-OF-PLANE
MOMENTS
The design adequacy of SC panel sections subjected to the
three in-plane required membrane strengths (Srx, Sry, Srxy)
and three out-of-plane required flexural or twisting strengths
(Mrx , Mry , Mrxy) needs to be evaluated. ANSI/AISC N690
requires this evaluation for each notional half of the SC
section that consists of one faceplate and half the concrete
thickness. ANSI/AISC N690 limits the interaction for each
notional half by Equations A-N9-24 to A-N9-26. The equations utilize the maximum and minimum required principal
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in-plane strengths for the notional half of the SC panel section, Sr,max and Sr,min, calculated using Equations A-N9-27 to
A-N9-30. Alternately, for each notional half, the interaction
can be limited directly with the required in-plane membrane
strengths per unit width (Srx′ , Sry
′ and Srxy
′ ), using Equations
′ and Srxy
A-N9-31 to A-N9-33. The values of Srx′ , Sry
′ are calculated using Equations A-N9-28 to A-N9-30.
The combined in-plane forces (Srx, Sry, Srxy) and out-ofplane moments (Mrx, Mry, Mrxy) are shown in Figure 9-2(a).
The interaction equations were developed based on the conservative simplified design approach developed by Varma
et al. (2014), which consists of (1) dividing the SC panel
section into two notional halves, (2) calculating the required
in-plane strengths (Srx′ , Sry′ and Srxy
′ ) for each notional half,
and (3) calculating the required in-plane principal strengths
(Sr,max and Sr,min) for each notional half.
Each notional half consists of one faceplate and half
the concrete infill thickness as shown in Figure 9-2(b).
The required in-plane strengths (Srx′ , Sry
′ ) for each
′ and Srxy
notional half are calculated by representing the out-of-plane
moments as force couples with effective arm lengths: 0.90
times the wall thickness for tension dominated situations
with significant concrete cracking and 0.67 times the wall
thickness for compression dominated situations with limited
concrete cracking. The required in-plane principal strengths
(Sr,max and Sr,min) can be calculated for each notional half
using the required in-plane strengths (Srx′ , Sry
′ ) and
′ and Srxy
appropriate equations.
Varma et al. (2014) developed a conservative simplified
interaction surface in principal force space for checking the
design adequacy of the notional halves of the SC wall panel
section. As shown in Figure 9-3, the interaction surface has
four regions in principal force space:
avg
Fig. 9-1. Unit cell for calculating Qcv (Bhardwaj et al., 2017).
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(a) Forces on panel section
(b) Forces on notional halves
Fig. 9-2. Combined forces acting on panel section and notional halves (Varma et al., 2014).
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(1) region I = biaxial tension
(2) region II = axial tension + in-plane shear
(3) region III = axial compression + in-plane shear
(4) region IV = biaxial compression
The interaction surface and these four regions are defined
by anchor points located at 50% of the total section strengths
in uniaxial tension, biaxial tension, pure in-plane shear, uniaxial compression, and biaxial compression. The 50% reduction reflects that the interaction surface was for each notional
half of the SC panel section. The interaction equations for
each of these four regions are also provided in Varma et al.
(2014).
For further simplification, regions I and II were combined
into one region described by a straight line connecting the
anchor points of pure shear and biaxial tension in the principal force space. This conservatively eliminated the uniaxial tension as an independent anchor point and reduced the
number of regions and equations needed for the interaction
surface.
As shown in Figure 9-4, the uniaxial tensile strength is
conservatively adjusted to be collinear with the straight line
joining the anchor points of pure in-plane shear and biaxial
tension in principal force space. This is always slightly conservative because of several reasons: The pure in-plane shear
strength is always less than or equal to AsFy / 2; the biaxial
tension point is anchored at AsFy / 2; and the resistance factors are less than or equal to one, whereas the corresponding
safety factors are greater than one. Therefore, the resulting
unaxial tension anchor point will be slightly less than AsFy / 2.
The resistance and safety factors for available demands
for the notional halves are less conservative than those for
the corresponding individual demands on the panel sections
because the maximum individual required tensile and shear
demands will rarely occur in the same panel section.
Varma et al. (2014) confirmed the conservatism of the
design approach by developing an MBM that accounts for
the complex behavior of the composite SC panel section subjected to combined in-plane forces and moments, and also
by developing a detailed nonlinear inelastic finite element
model of SC panel sections subjected to combined in-plane
forces and moments. Figure 9-5 confirms the conservatism
of the design approach by comparing the bending moment
and in-plane shear (Mrx, Srxy) interaction predicted for an SC
panel section by all three methods: design approach, MBM,
and finite element model. As shown, the design approach is
very conservative.
The alternate interaction equations of ANSI/AISC N690
were obtained by recasting the interaction equations, which
are in terms of the principal force Sr,max and Sr,min, directly
into terms of Srx′ , Sry′ and Srxy
′ . The alternate interaction equations mathematically represent the same interaction surface
Fig. 9-3. Interaction surface for in-plane forces in principal force space (Varma et al., 2014).
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Fig. 9-4. Simplified interaction surface plotted in principal force space.
Fig. 9-5. Moment-shear interaction for SC wall (Varma et al., 2014).
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as the original interaction equations in terms of the principal
forces. This was confirmed by plotting the interaction surface using both forms of the interaction equations.
Figure 9-6 shows the interaction surface defined by the
interaction equations in terms of the principal forces and
some data points that were obtained using the alternate
forms of the interaction equations, which confirms their
equivalency. Figure 9-6 was developed using 0.5-in.
(13 mm)-thick faceplates made from 50-ksi (350 MPa) steel
filled with 29 in. (725 mm) of 6-ksi (40 MPa) concrete to
develop a 30-in. (750 mm)-thick SC wall panel section. The
anchor points in Figure 9-6 are without phi factors.
Fig. 9-6. Interaction surface and data points using alternate forms of interaction equations.
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Chapter 10
Demand Capacity Ratios and Interaction Surfaces
For each loading combination, the SC wall design needs to
be checked for both individual force demands and combined
force demands. The demand capacity ratios (DCRs) for all
elements of the SC walls need to be calculated for each load
combination. For combined force demands, the principal
force pairs are plotted on the interaction surface—the boundary region based on the limiting values of the combination
of demands. The DCR can then be calculated by measuring
the distance to the failure surface, considering the loading to
be proportionally incremental. The interaction can also be
checked by satisfying the interaction equations, Equations
A-N9-23 and A-N9-24 to A-N9-26, provided in ANSI/AISC
N690.
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Chapter 11
Design of SC Wall Connection
SC wall connection regions are defined in Section 7.6. The
concept of connection regions for SC walls is similar to
that of load transfer regions for composite columns specified by AISC Specification Section I6 (AISC, 2010b). The
connection regions of SC walls are designed and detailed
according to ANSI/AISC N690, Section N9.4. Bolting and
welding are used as connection elements in steel structures;
column anchorages involve base plates, anchor rods and
shear lugs. Well-established rules and methods exist for sizing these connections. Embedded rebar, shear-friction rebar,
and joint ties are used as connection elements across RCto-RC joints—often construction joints—and again, established rules exist for designing RC connections. These rules
for steel and RC structures are applicable to specific configurations, details or elements of SC wall connections; for
example, the faceplates for SC wall-to-wall connections can
be designed and detailed according to guidelines for steel-tosteel connections. Some general guidelines for various types
of connections follow.
For steel-to-steel connections, bolts and welds can be easily sized and installed to provide adequate strength; that is,
to match the required strengths or the capacity of the connecting elements. Assuring adequate ductility, especially in
seismic applications, sometimes requires further consideration and testing to ensure that the connecting elements are
able to accommodate large inelastic deformations in the connected members [e.g., post-Northridge research of moment
frame connections and development of the AISC standard,
Prequalified Connections for Special and Intermediate Steel
Moment Frames for Seismic Applications (AISC, 2010a)].
For bracing connections or extended plate connections,
simple empirical methods exist, such as the uniform force
method, that are adequate for design instead of having to
perform design using complex finite element analyses.
For anchorage of linear steel components, linear steel
members, such as columns, can be anchored into concrete
using anchor rods and lugs. This is a case of connection
between linear steel members and RC elements, such as
piers and basemats. Anchor rods are typically used to resist
pullout forces and bending moments, while lugs are used
to resist shear forces. Design rules are based on tests that
exist for sizing anchor rods—ACI 349-06, Appendix D
(ACI, 2006)—and lugs—AISC Design Guide 2 (Darwin,
1990). Demands on connecting elements due to simultaneous forces and moments acting on the anchored member can
be easily determined for adequate sizing.
For connections to RC elements, linear or continuum
RC elements, such as beams/columns and walls/floors, are
often connected with other RC elements, usually across
construction joints. Typical connecting elements are dowels. Dowels act as splices for transfer of tension and bending moments, and they act as shear-friction reinforcement
for transfer of shear forces. Closely spaced ties are used to
achieve high strain capacity and high shear strength within
the beam-column joints. Substantial test data and prescriptive design rules exist to adequately size RC connections.
Generally, no prescriptive rules exist for designing connections between linear composite members and RC elements, such as filled composite column anchorage. However,
various types of connection elements can be used to connect composite members and RC members, including posttensioned bars or strands, steel headed stud anchors, dowels,
lugs, and anchor rods. Possible interaction due to simultaneously acting forces and moments needs to be considered
when sizing the connecting elements. The behavior of connecting elements under cyclic loads such as seismic loading
needs to be considered.
SC connections are more complicated than connections
involving linear composite members because multiple types
of demands exist on plate/shell type SC elements. Unlike
RC walls, SC walls have very large required in-plane shear
strength; use of shear friction reinforcement alone may not
be sufficient to match the required strength. Various types of
connecting elements may be used to resist various demands;
however, often the same type of connecting element may
resist different types of demands simultaneously. Unlike RC
member connections, it is not easy to embed rebar in SC
walls because it is in the form of continuous faceplates.
Behavior beyond SSE performance needs to be considered, especially if the connection involves a brittle failure
mode or if the design needs to satisfy a review level earthquake—a representation of an earthquake ground motion in
the form of a response spectrum, applied at a certain depth
or location, used as the basis for the analyses performed in a
seismic margin assessment. It is possible that the connection
will need to be designed to be weaker than the connected
elements, particularly for in-plane shear. Adequate inelastic
deformation capacity will need to be specified. Interaction
due to various types of demands will need to be accounted
for, preferably on a small element basis in the range of two
times the SC wall thickness, rather than considering the
entire SC wall as one unit. The local and global ductility
requirements need to be addressed. Local ductility in the
connection regions can be achieved by following the minimum requirements and detailing provisions of ANSI/AISC
N690. Global ductility can be achieved by choosing the
appropriate connection design philosophy.
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11.1
CONNECTION DEMAND TYPES
Connection demands can be obtained from finite element
(FE) analyses conducted in accordance with ANSI/AISC
N690, Section N9.2. Elastic finite element (EFE) analyses
are conducted for static loading conditions, and for Condition A (operating thermal + seismic loading) and Condition
B (accident thermal + seismic loading), using appropriate
stiffness values accounting for the effects of concrete cracking where applicable (discussed in Sections 7.1 and 7.5). A
summary of the applicable loading combinations typically
considered is provided in the design example in Appendix A
in Table A-1. The results from the FE analyses can be used to
determine the design demands per unit length of the connection, depending on the connection design philosophy, which
are membrane axial force, Nu, membrane in-plane shear
force, Vuin, out-of-plane shear force, Vuout, and out-of-plane
bending moment, Mu. These are illustrated in Figure 11-1.
Based on the connection design philosophy, each connection
design demand may need to be differentiated into demands
due to seismic loading (Condition A or B), and demands due
to nonseismic loading, such as static loads and thermal loads.
11.2
FORCE TRANSFER MECHANISM
For each of the required strengths, Nr , Vuin, Vuout or Mr , a
clearly identifiable force transfer mechanism needs to be
identified. Each force transfer mechanism involves connectors of the same type in the connection region. If more
than one force transfer mechanism is possible for resisting
a particular demand type, the one with the largest connection design strength is the governing force transfer mechanism. Commonly used connectors include steel headed stud
anchors, anchor rods, ties, reinforcing bars and dowels, posttensioning bars, shear lugs, embedded steel shapes, welds
and bolts, rebar mechanical couplers, and direct bearing in
compression. Direct bond transfer between the steel plate
and the concrete is not considered as a valid connector or
force transfer mechanism.
11.3
CONNECTION DESIGN PHILOSOPHY AND
REQUIRED STRENGTH
Capacity design is a fundamental aspect of the seismic
design philosophy for structures (ASCE, 2013). It can be
achieved by (1) designing the connections to be stronger
than the expected strength of the weaker of the two connected parts, which is considered a full-strength connection,
or (2) detailing the connected parts to have adequate ductility to undergo inelastic deformations and dissipate energy
for beyond design basis events, which is considered an overstrength connection. ANSI/AISC N690, Section N9.4.2, permits design of SC wall connection regions using either of
the philosophies. However, full-strength connections are the
preferred option. The connection designed according to one
of these philosophies—full-strength or overstrength connection—is further evaluated for the combined force demands
for the load combinations, as shown in Figure 11-1. This
design approach ensures that the connections are typically
stronger than the weaker of the connected parts, and the
structure will have ductile failure modes occurring in the SC
walls, not in the associated connections, governing the overall response if the SC wall becomes overloaded. Figure 11-2
presents the procedure for determining the required strength
of a connection. The two connection design philosophies are
discussed in the following paragraphs.
11.3.1 Full-Strength Connection Design
The full-strength connection design philosophy develops
the expected strength of the weaker of the two connected
parts. The connection ensures ductile behavior with yielding
and inelasticity occurring away from the connection in one
of the connected SC walls or RC slabs. This ductile design
approach is consistent with the concrete anchorage design
provisions given in Section D.3.6.1 of ACI 349-06.
A full-strength connection is designed to transfer 1.25
times the individual nominal strengths—axial tension, inplane shear, out-of-plane shear, or bending moment—of the
weaker of the two connected parts. A load increase factor
Fig. 11-1. Connection design demands per unit length.
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(LIF) of 1.25 is selected to be consistent with ACI 349-06
requirements, which is the prevalent code for design of
safety-related nuclear concrete facilities. The regulatory
agency also considers the precedence established by ACI
349-06 to be the relevant rubric for evaluating and accepting SC structures currently being built in the United States,
which are primarily replacements for RC structures. This
factor takes into consideration the strain hardening and overstrength that will be expected in SC walls. Clearly identifiable force transfer mechanisms are used to transfer each of
the individual strengths. These force transfer mechanisms
involve connectors that are well established in practice; for
example, steel welding, welded rebar couplers, and direct
shear. The available strength of the connectors is determined
using applicable design codes as mentioned in ANSI/AISC
N690, Section N9.4.3.
Additionally, the full-strength connection is checked for
the design force and moment demands calculated from the
EFE analyses of the connected elements for design basis
load combinations. These design force and moment demands
are assumed to occur concurrently, which is conservative.
The connection adequacy is assessed by first calculating
the concurrent superimposed demands on the connectors
that are involved in the force transfer mechanisms for the
design force and moment demands, and then checking the
connector strength while accounting for interaction effects
in accordance with load combinations according to Section
7.1. For certain connection types such as basemat anchorage
connections, ACI 349-06 or ASME Boiler & Pressure Vessel Code Section III, Division 2 (ASME, 2013) may also be
applicable.
In summary, the full-strength connection is designed to
have predominantly elastic behavior and adequate strength
for design basis loads and load combinations. It is further
designed to be stronger than the expected strengths of the
weaker of the connected parts. Therefore, for beyond design
basis loads and load combinations, inelastic deformations
and energy dissipation will occur in the weaker of the connected parts. The connected parts are detailed accordingly to
have good ductility and to prevent nonductile failure modes,
such as out-of-plane shear and SC specific failure modes.
Full-strength connection design can provide acceptable performance for accident thermal loading events, as inelastic
behavior and ductility at elevated temperatures is expected
from the connected SC wall and not the connections. SC
walls are expected to have good behavior and ductility for
accident thermal events. The connection can be verified analytically and experimentally. Because the failure is expected
Fig. 11-2. Calculation of connection required strength.
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to occur in the connected SC walls or RC walls, only one or
two scaled tests may be needed to confirm and demonstrate
the ductile inelastic behavior. In some cases, analytical verification by means of benchmarked models may be sufficient.
11.3.2
Overstrength Connection Design
In some limited situations, it is not feasible to provide a
full-strength connection. For example, a full-strength connection design may not be feasible if the associated SC wall
or RC slab is significantly overdesigned with respect to the
EFE calculated force and moment demands due to radiation shielding requirements. In such cases, the connection
is designed to provide direct overstrength in the connection design with respect to the calculated force and moment
demands. The overstrength connection design philosophy,
adopted here, requires the connection to be designed for
200% of the seismic demands plus 100% of the nonseismic
demands calculated from EFE analyses of the SC wall structure for loads and load combinations. The goal of this connection design philosophy is to provide high confidence of
low probability of failure (HCLPF) for 1.67 times the SSE,
which is accomplished conservatively by increasing the SSE
force and moment demands by a factor of 2.0. This LIF factor of 2.0 achieves the seismic margin of 1.67 while accounting for the slight difference in the failure probability levels
required by HCLPF and those provided inherently by ACI
349-06 or similar code equations for component or connector strength.
Overstrength connections are expected to fail before the
connected SC walls. Therefore, these connections have to
be checked for the simultaneous actions of amplified design
demands calculated from FE analysis of loading combinations. This can be complicated as the simultaneous demands
will subject the connectors to a combination of stresses. The
connections will have to be evaluated for accident thermal
loading scenarios and thermal gradients producing concrete
cracking. Additionally, experimental verification of overstrength connections will be challenging as the failure will
be nonductile. The connection behavior needs to be verified
for various demand combinations and thermal loading.
It is important to note that the overstrength connection
design philosophy should be used only in limited situations where a full-strength connection cannot be provided.
Further­more, the overstrength connection design philosophy
should preferably be used only for the particular force transfer mechanisms in the connection that cannot be designed
to achieve the full strength of the connected wall. Additionally, all connectors utilized in overstrength connection force
transfer mechanisms need to be designed to exhibit ductile
failure modes involving steel yielding.
11.3.3
Connection Evaluation for Combined Forces
The connections designed using either of the connection
design philosophies need to be checked for the combination
of the individual force demands discussed in Section 11.1—
Nu , Vuin, Vuout and Mu. The force transfer mechanisms discussed in Section 11.2 are used with these individual force
demands to determine the required strengths for the contributing connectors. The total required strength, Ru , for the
connectors is calculated as the superposition of the required
strengths from all the individual demands.
The total required strength is compared with the connector available strengths, ϕRn, calculated as described in Section 11.4, while accounting for the effects of superposition
of force demands as applicable. For example, rebar anchors
may be subjected to superposition of tension and shear
forces, the interaction of which is considered explicitly.
Note that some connections may be governed by more
than one code. For example, the SC wall-to-basemat anchorage connection is governed by ANSI/AISC N690 and liner
design requirements of the ASME Boiler & Pressure Vessel
Code Section III, Division 2, which is applicable when the
SC wall is a part of the nuclear containment structure. These
connections need to meet the requirements of all applicable
codes.
11.4
CONNECTION AVAILABLE STRENGTH
The connection design strengths—ϕNn , φVnin, φVnout and
ϕMn—for each of the corresponding connection required
strengths—Nr , Vrin, Vrout, Vrout and Mr —are calculated using
the applicable force transfer mechanism identified and the
design strength of its contributing connectors. The available
strength of the connectors is determined according to Section N9.4.3 of ANSI/AISC N690. The available strength of
the connection is determined as shown in Figure 11-3.
11.4.1
Connector Available Strength
For a force transfer mechanism, the available strength of
the contributing connectors is determined based on the
following:
(a) For steel headed stud anchors, the available strength is
determined in accordance with AISC Specification Section I8.3 (AISC, 2010).
(b) For welds and bolts, the available strength is determined
in accordance with AISC Specification Chapter J.
(c) For compression transfer via direct bearing on concrete,
the available strength is determined in accordance with
AISC Specification Section I6.3a.
(d) For the shear-friction load transfer mechanism, the available strength is determined in accordance with ACI 34906, Section 11.7.
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(e) For embedded shear lugs and shapes, the available
strength is determined in accordance with ACI 349-06,
Appendix D.
(f) For anchor rods, the available strength is determined
from ACI 349, Appendix D.
11.5
SC WALL-TO-BASEMAT ANCHORAGE
CONNECTION
The SC wall-to-basemat connections can be detailed differently depending on project-specific design considerations
and site conditions. The connections may be designed as fullstrength or overstrength connections. Three typical configurations of the SC wall-to-basemat connections are discussed
here. Each connection configuration is discussed along with
possible force transfer mechanisms. The adequacy of the
connection, considering the connection is designed as a fullstrength connection, is checked for individual demand types
corresponding to 1.25 times the available strength of the SC
wall. The connection is additionally checked for a combination of demands, obtained from finite element analysis, in
the wall for different load combinations.
11.5.1
Single Base Plate Connection
The single base plate SC wall-to-basemat connection consists of a base plate welded to the faceplates of the SC wall.
The base plate is connected to the concrete infill of SC wall
by means of steel anchors and to the basemat by means of
welded coupled bars. The connection layout is presented in
Figure 11-4(a). Typical connection detailing is presented
in Figure 11-4(b). The design of a full-strength single base
plate SC wall-to-basemat connection is presented in Step 12
of the design example in Appendix A.
The force transfer mechanism for individual demand types
is discussed in the following. The section discusses only one
force transfer mechanism for each demand type. However,
more than one force transfer mechanism may be possible for
some demand types, in which case the one with the largest
connector design strength will be the governing mechanism.
Tensile Force Demand
The available tensile strength of the SC wall is governed by
the resistance of the faceplates. The SC wall-to-base plate
weld needs to be designed for 1.25 times the available tensile strength of the SC wall. The force transfer mechanism
is illustrated in Figure 11-5. As shown, the SC faceplate-tobase plate weld needs to resist the tensile demand of the SC
wall. The mechanism conservatively considers that there is
no force transfer through the steel anchors at the SC concrete
infill base plate interface. The force in the base plate will be
transferred to the concrete basemat by means of anchor rods
welded to base plate and embedded in the basemat concrete.
The base plate will also be designed for any bending stresses
based on the configuration of anchor rods.
Compression Demand
The compression strength of the SC wall-to-basemat connection is governed by the faceplate and concrete compressive
Fig. 11-3. Calculation of connection available strength.
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strengths. The base plate needs to resist the bearing forces
transferred from the SC wall. Further, the bearing force will
transfer from the base plate to the basemat. The force transfer
mechanism is illustrated in Figure 11-6. The limit states of
bearing for the concrete and yielding for the base plate need
to be checked for this force transfer mechanism (Fisher and
Kloiber, 2006). Any cantilever bending in the base plate due
to the reaction from basemat also needs to be considered.
In-Plane Shear Demand
The in-plane shear strength of the SC wall-to-basemat connection is governed by the available shear strength of the
steel anchors and the friction force between the base plate
and the basemat concrete. The in-plane shear demand in the
SC wall is transferred to the base plate by means of steel
anchors. The fraction of the in-plane shear demand carried
by the faceplates is transferred to the base plate through the
faceplate-to-base plate connection, typically a welded connection. The demand is then transferred to the basemat by
means of shear friction force between the base plate and
the basemat. The force transfer mechanism is illustrated
in Figure 11-7. Other force transfer mechanisms may also
be considered for transfer of force from the base plate to
the basemat; for example, shear lugs or concrete bearing on
rebar couplers.
(a) Connection layout
(b) Cross-section view of connection
Fig. 11-4. Single base plate SC wall-to-basemat connection.
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Out-of-Plane Shear Demand
The out-of-plane shear strength of the SC wall-to-basemat
connection is governed by the available shear strength of the
steel anchors and the friction force between the base plate
and the basemat concrete. For a full-strength connection, this
demand may be associated with developing the out-of-plane
plastic available flexural strength of the section. The force
transfer mechanism for out-of-plane shear force demands is
presented in Figure 11-8. The force transfer mechanism is
the same as for in-plane shear demands. Alternatively, the
force transfer can be considered to be achieved through a
diagonal compression strut anchored at the bottom corner
of the faceplate/base plate interface. Because this strut-tie
mechanism involving the tie-bars and infill concrete does
not involve standard connectors, the existence of this mechanism may need to be confirmed by experiments or relevant
literature.
Out-of-Plane Flexural Demand
The force transfer mechanism for out-of-plane flexure is
illustrated in Figure 11-9. As shown in the figure, the outof-plane flexural demand can be considered as an equivalent
force couple acting on the faceplates. The resulting tension
and compression forces in the faceplates are transferred to
the basemat by means of the force transfer mechanisms for
tension and compression demands discussed earlier.
Fig. 11-5. Force transfer mechanism for tensile demand.
Fig. 11-6. Force transfer mechanism for compression demand.
Fig. 11-7. Force transfer mechanism
for in-plane shear demand.
Fig. 11-8. Force transfer mechanism
for out-of-plane shear demand.
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11.5.2
Split Base Plate Connection
The split base plate SC wall-to-basemat connection is a
variant of the single base plate connection, wherein two
separate base plates are provided instead of a single base
plate. Typical layout of the connection is presented in Figure 11-10. Because there is not enough interface between
the base plates and the SC concrete infill, no steel anchors
are provided. The split base plate connection is economical
considering the typical thickness of SC wall (3–5 ft). The
force transfer mechanisms for tension and out-of-plane flexural demands are the same as in single base plate connections. For the compression demand, the compression force in
the SC wall concrete infill is transferred in bearing directly
to the basemat concrete. The force transfer mechanisms for
in-plane and out-of-plane shear demands is shear friction at
the interface of the SC concrete infill and the basemat concrete. Other force transfer mechanisms such as shear transferred through the base plate and anchoring rebar may be
considered.
11.5.3
Rebar SC Wall-to-Basemat Connection
The rebar SC wall-to-basemat connection employs reinforcement bars to transfer SC wall demands to the basemat. The
connection is similar to those for RC wall-to-basemat connections. The details of the connection can be varied depending on if the connection is full-strength or overstrength and
constructability concerns. An overstrength connection may
be accomplished by leaving reinforcing bars projecting from
the concrete basemat. The empty SC module is assembled
around the reinforcing bars, and the concrete is then cast.
The SC infill concrete can also be cast monolithically with
the basemat. The faceplates can either be embedded into the
basemat or be terminated at the surface of the basemat. The
connection detail with faceplates embedded is presented in
Figure 11-11. However, this detail is difficult to construct
as the faceplates may interfere with basemat reinforcement.
Additionally, embedding faceplates may result in the faceplates participating in some force transfer mechanisms. This
may increase the embedment depth required for these faceplates, thus increasing the difficulty in construction. The second option of ending the faceplates at the surface base plates
is easier to construct. However, in this case, the bottom portion of the SC wall behaves as an RC wall. This type of connection may be employed for overstrength design because
achieving the full-strength of the SC wall through a connection that essentially behaves as an RC wall-to-basemat
conncection may result in very heavy reinforcement. The
high amount of reinforcement may adversely affect the constructability of the connection.
Tensile Demand
The tensile demand in the SC wall is transferred to the basemat by means of direct tension in the reinforcement bars.
The tensile demand in the SC wall is primarily carried by the
faceplates. This force demand is transferred to the concrete
infill in the SC-to-RC transition region through faceplate
steel headed stud anchors. The force is then transferred to
the reinforcing bars through bond. The force transfer mechanism is shown in Figure 11-12. The amount of reinforcement is determined based on the tensile demand. Sufficient
Fig. 11-9. Force transfer mechanism
for out-of-plane moment demand.
Fig. 11-10. Typical connection layout for
split base plate SC wall-to-basemat connection.
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embedment length of reinforcement bars (lap splice length
per ACI 349) is provided to develop the tensile strength of
the bars.
Compression Demand
The compression demand in the SC wall is transferred to
the basemat in bearing. The limit state of bearing for concrete needs to be checked for this force transfer mechanism
(Fisher and Kloiber, 2006).
Fig. 11-11. Typical connection layout for
rebar SC wall-to-basemat connection.
(a) Load transfer using rebar direct shear
In-Plane Shear Demand
The in-plane shear demand of the SC wall is transferred to
the basemat through shear friction between infill concrete
and the basemat concrete. The shear forces in the faceplates
are transferred to the concrete infill through the faceplate
steel headed stud anchors. The force transfer mechanism
is shown in Figure 11-13. Direct shear in the rebar—shear
force transferred from the SC wall directly to the basemat
rebar—also needs to be checked in order to avoid failure of
the connection.
Fig. 11-12. Force transfer mechanism for tensile demand.
(b) Load transfer using shear friction
Fig. 11-13. Force transfer mechanism for in-plane shear demand.
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Out-of-Plane Shear Demand
Axial Tensile Demand
The force transfer mechanism for out-of-plane shear is the
same as for the in-plane shear demand.
Full-strength connection design corresponds to the development of a plastic mechanism accompanied by the formation
of plastic hinges in the continuous SC wall at locations outside the joint region as shown in Figure 11-16. This plastic mechanism will provide ductility and energy dissipation
for beyond design basis events and will limit the maximum
axial tension for which the joint needs to be designed. If
M pexp−c is the expected plastic flexural strength of the continuous SC wall, the maximum axial tension, Nr , that can
be transferred through the joint will be equal to four times
M pexp−c divided by the length, L, of the continuous SC wall,
as shown in Figure 11-16. The length, L, is the clear span of
the wall between the supports. This maximum axial tension,
Nr , is the connection required strength in axial tension. The
joint region will need to be designed for the forces and joint
shears, Vjs, associated with connection required strength, Nr ,
in axial tension. The force transfer mechanism due to axial
tensile strengths is shown in Figure 11-17. The various connector elements need to be designed for the demands corresponding to the force transfer mechanism.
Out-of-Plane Flexural Demand
The out-of-plane available flexural strength of the connection may be idealized as a plastic compression mechanism
in the basemat concrete—concrete in compression reaches
its capacity—and tension forces in the reinforcement bars
on the opposite side. The force transfer mechanism is shown
in Figure 11-14. Adequate resistance and development
length of the rebar need to be provided to transfer the force
demands from the SC walls to the concrete basemat.
11.6
SC WALL-TO-WALL JOINT CONNECTION
The internal forces generated in SC walls by the load combinations are either anchored to the basemat or transferred
to connected walls through joints. The SC wall-to-basemat
connection has been discussed previously. Figure 11-15
presents the plan view of a typical SC wall-to-wall joint connection. The connection can be designed as a full-strength or
overstrength connection.
The typical SC wall-to-wall T-joint connection consists of
a discontinuous SC wall that is connected to an orthogonal
continuous SC wall. The force demands need to be transferred from the discontinuous SC wall to the continuous SC
wall through the joint region. For a full-strength connection,
the individual demand types can be transferred by considering the following force transfer mechanisms.
In-Plane Shear Demand
Full-strength connection design requires the transfer of
expected in-plane shear strength, Vni -exp- dc, which is the
design in-plane shear demand, of the discontinuous SC wall
to the continuous SC wall. The various connector elements
in the joint region need to be designed for the forces and
joint shear demands associated with the mechanism shown
in Figure 11-18.
Out-of-Plane Shear Demand
Full-strength connection design requires the transfer of the
expected out-of-plane shear strength, Vno-exp- dc, which is the
design out-of-plane shear demand, for the connection of
the discontinuous SC wall as shown in Figure 11-19. The
various connector elements in the joint region need to be
designed for the forces and joint shear, Vjs, demands associated with the mechanism shown in Figure 11-20.
Out-of-Plane Flexural Demand
Fig. 11-14. Force transfer mechanism
for out-of-plane flexural demand.
Full-strength connection design requires the transfer of the
expected out-of-plane flexural strength, M pexp− dc, which is
the design out-of-plane flexure demand, of the discontinuous
SC wall. The mechanism corresponds to the development
of a plastic hinge in the discontinuous SC wall as shown in
Figure 11-21. This plastic hinge will provide ductility and
energy dissipation for beyond design basis events. The various connector types in the joint region need to be designed
for the forces and joint shear demands associated with the
transfer mechanism shown in Figure 11-22.
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Joint Shear Demand
The joint region for SC wall-to-wall connection is designed
to be stronger than the connected walls. The region is shown
in Figure 11-15. The design consists of steel diaphragm
plates, steel anchors, and tie bars. The steel diaphragm
plates confine the concrete and the region can be treated as
a filled composite columns. The joint region is designed for
the forces and joint shears, Vjs, associated with the transfer of each demand type. The joint shears produced by the
force transfer mechanisms are presented in Figure 11-17
(due to tensile demand), Figure 11-20 (due to out-of-plane
shear demand), and Figure 11-22 (due to out-of-plane flexural demand). Seo et al. (2013) and Seo (2014) conducted
experimental studies that observed the joint behavior for SC
wall-to-wall connections. The studies found that significant
joint shear is induced by the out-of-plane shear and flexural
demands. Seo et al. observed that the joint shear strength can
be conservatively predicted by ACI 349-06, Section 21.5.3,
considering the value of γ as 12 for an SC wall-to wall joint.
11.7
RC SLAB-TO-SC WALL JOINT
CONNECTION
Figure 11-23 presents a typical RC slab-to-SC wall connection detail. One conceptual design of the connection is
presented in Figure 11-24. The connection can be designed
as a full-strength or overstrength connection. The connection consists of a discontinuous RC slab that is connected to
an orthogonal continuous SC wall at both sides. The force
demands need to be transferred from the discontinuous RC
slab to the continuous SC wall through the joint region. For
a full-strength connection, the individual demand types can
be transferred by considering the following force transfer
mechanisms.
Axial Tensile Demand
Axial tension is transferred from the RC slab to the SC wall
through a load path consisting of rebar, rib plates and/or
ties, which are in direct tension. The tensile demand type is
shown in Figure 11-25. The load transfer connectors need
to be developed adequately to transfer the factored demand.
In-Plane Shear Demand
Steel anchors welded to the outside of the SC wall embedded
in the RC slab and the anchors located on the inside of the
SC wall provide the direct load path for the in-plane shear
demands. Figure 11-26 shows the in-plane shear demand
type for the connection. Shear friction resulting from engaging slab rebar at the SC faceplate provides an additional,
independent, full-strength force transfer mechanism.
Fig. 11-15. Typical SC wall-to-wall joint connection.
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Fig. 11-16. Failure mechanism due to tensile demand in the discontinuous SC wall (Seo, 2014).
⎛
⎝
⎞
j ⎠
Fig. 11-17. Force transfer mechanism due to tensile strength (Seo, 2014).
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Fig. 11-18. Load transfer mechanism for in-plane shear demand.
Fig. 11-19. Moments and shears due to design out-of-plane shear demand (Seo, 2014).
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Fig. 11-20. Force transfer mechanism for out-of-plane shear demand (Seo, 2014).
Fig. 11-21. Failure mechanism due to out-of-plane flexural demand on discontinuous SC wall (Seo, 2014).
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Out-of-Plane Shear Demand
Out-of-Plane Flexural Demand
Figure 11-27 shows the out-of-plane shear demand for the
connection. Steel anchors welded to the outside of the SC
wall embedded in the RC slab and the anchors located on
the inside of the SC wall provide the direct load path for the
out-of-plane shear demands. Shear friction resulting from
engaging the slab rebar at the SC faceplate provides an additional, independent, full-strength force transfer mechanism.
Figure 11-28 shows the out-of-plane flexural demand for the
connection. The tensile demand resulting from the out-ofplane moment is transferred from the slab to the SC wall
through direct tension in rebar, rib plates and/or ties. The
resulting compression force is mainly transferred through
concrete in bearing.
The out-of-plane flexural demand will lead to a joint shear
demand for the connection, as shown in Figure 11-28. The
demand is resisted by the concrete joint shear capacity determined by ACI 349-06, Section 21.5.3.
⎛
⎝
⎞
⎠
Fig. 11-22. Force transfer mechanism for out-of-plane flexural demand (Seo, 2014).
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Fig. 11-23. Typical RC slab-to-SC wall joint connection.
Fig. 11-24. Conceptual details of SC wall-to-RC slab connection.
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Fig. 11-25. Axial tension strength demand for RC slab-to-SC wall joint.
Fig. 11-26. In-plane shear strength demand for RC slab-to-SC wall joint.
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Fig. 11-27. Out-of-plane shear strength demand for RC slab-to-SC wall joint.
Fig. 11-28. Out-of-plane flexural demand and joint shear demand for RC slab-to-SC wall joint.
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Chapter 12
Impactive and Impulsive Loads
The design of SC walls for safety-related nuclear facilities may need to be checked for impactive loads, such as
tornado-borne missiles, whipping pipes, aircraft missiles, or
other internal and external missiles, and for impulsive loads,
such as jet impingement loads, blast pressure, compartment
pressurization, or jet shield reactions. The effects for impactive and impulsive loads are considered in extreme environmental and abnormal load combinations concurrent with
other loads. These effects are permitted to be determined
using inelastic analysis with limits on the ductility ratio
demand, μdd, defined as the ratio of maximum displacement
from analysis to the effective yield displacement in ANSI/
AISC N690, Equation A-N9-7, as given in Table 12-1. Yield
displacement is established using the cross-sectional effective flexural stiffness for analysis, EIeff, according to ANSI/
AISC N690, Equation A-N9-8.
The ductility of the member at failure is more dependent on the failure mode than on the type of loading. This
is observed in the values of ductility ratios in Table 12-1. A
ductility ratio greater than 1.0 is permitted for brittle failure
modes because even brittle structures have been observed to
display some inelastic deformation capabilities.
The available strength of SC walls for impulsive and
impactive loads may be governed by flexural yielding or outof-plane shear failure. ANSI/AISC N690 Appendix N9 classifies SC walls as flexure-controlled if the available strength
for the limit state of flexural yielding is less than the available strength for the limit state of out-of-plane shear failure
by at least 25%. Otherwise, SC walls are classified as shearcontrolled. This requirement is based on the fact that the
increase in strength under rapid strain exhibited by steel is
better established than that for the shear strength of concrete.
Careful consideration should be given to special cases where
the flexural behavior goes significantly past yield into the
strain-hardening range. In such cases, the margin for available strength in shear over the available strength in flexure
should be higher.
ANSI/AISC N690 Appendix N9 permits dynamic increase
factors (DIFs) based on the strain rates involved to be applied
to static material strengths of steel and concrete for purposes
of determining section strength. However, the DIF values
are limited by ANSI/AISC N690, Table N9.1.1. The DIF
is limited to 1.0 for all materials where the dynamic load
factor associated with the impactive or impulsive loading is
less than 1.2 (NRC, 2001). Plastic hinge rotation capacity
need not be considered if the deformation limit is kept under
10 for flexure controlled sections (Varma et al., 2011c). For
the axial ductility ratio, the effective yield displacement is
calculated using the cross-sectional effective axial stiffness.
This axial stiffness is calculated using the material elastic
modulus and the model section thickness calibrated in accordance with ANSI/AISC N690, Section N9.2.3.
At the rates of strain that are characteristic of certain
impactive and impulsive loads, both the concrete and the
structural steel exhibit elevated yield strengths, while the
strain at the onset of strain hardening and the tensile strength
increase slightly. The modulus of elasticity remains nearly
constant. The DIF values given in ANSI/AISC N690 represent the ratio of dynamic to static yield strengths or ultimate
strengths, and are direct functions of the strain rates involved.
The values have been taken from NEI 07-13 (NRC, 2011).
Response of SC walls subjected to impulsive loads can be
determined by one of the following methods:
a. The dynamic effects of impulsive loads are considered based on approximation of the wall panel as a
single degree of freedom (SDOF) elastic, perfectly
plastic system, where the resistance function and limiting ductility are defined as in ANSI/AISC N690,
Section N9.1.6b. System response is determined by
either a nonlinear time history analysis or, for welldefined impulse functions, rectangular and triangular
pulses, selected from established response charts such
as those in Biggs (1964).
b. The dynamic effects of impulsive loads are considered based on the approximation of the wall panel as a
SDOF system with bilinear stiffness. System response
is determined by a nonlinear time history analysis.
Either the ductility is limited as defined in ANSI/
AISC N690, Section N9.1.6b, or the plate principal
strain may be limited to 0.05.
c. The dynamic effects of impulsive loads are considered by performing a nonlinear FE analysis. The plate
principal strain is limited to 0.05.
In cases of impulsive and impactive loads that are
expected to deform the structure beyond its elastic limits,
the usefulness of load combinations given in ANSI/AISC
N690, Section NB, is rather limited. These combinations do
not provide any means of accounting for the additional work
done by the static loads, which may be present as the structure deforms beyond its effective yield point.
If the energy balance method is used, only the energy available to resist the impactive and impulsive loads should be
used. Alternatively, if an elastoplastic analysis is performed,
the effective ductility ratio, μ′, to be used in the analysis for
impactive and impulsive loading is given by Equation 12-1:
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Table 12-1. Ductility Ratio Demand
Description of Element
Ductility Ratio Demand, μdd
Flexure controlled SC walls
μdd ≤ 10
Shear controlled SC walls
(yielding shear reinforcement spaced at section thickness divided by two or smaller)
μdd ≤ 1.6
Shear controlled SC walls
(other configurations of yielding or nonyielding shear reinforcement)
μdd ≤ 1.3
For axial compressive loads
μdd ≤ 1.3
μ′ =
μ dd Dy − Ds
Dy − Ds (12-1)
where
Ds = displacement due to static loads, in. (mm)
Dy = displacement at yield, in. (mm)
μdd = ductility factor
The effective ductility ratio is to be used in conjunction
with the effective available resistance, which is equal to the
available resistance less the force due to static loads. Instead
of a more rigorous analysis, seismic forces can be conservatively treated as equivalent static loads in the analysis for
determining the adequacy of the structure for impactive and
impulsive loading.
Design of SC walls for impactive loads needs to satisfy the criteria for both local effects and overall structural
response. Local impact effects include perforation of the SC
wall. For a structural system to act as a missile barrier, the
member needs to be sufficiently thick to prevent perforation.
Bruhl et al. (2015a) have presented a three-step approach
to design an individual SC wall for a specific missile. The
evaluation procedure is explained in Figure 12-1. The front
surface faceplate is conservatively neglected in this analysis.
Thus, impact of a projectile on the concrete dislodges a conical concrete plug, which in turn impacts the rear faceplate.
Step 1. The design method involves first selecting a concrete
Fig. 12-1. Evaluation procedure for tearing of
SC panels against impact (Mizuno et al., 2005).
wall thickness, tc. An existing wall thickness can be used
to verify the protection afforded by a given wall. For new
designs, the concrete thickness can be obtained from governing design requirements or 70% of the thickness for an RC
wall determined using DOE-STD-3014 (DOE, 2006) or NEI
07-13 (NRC, 2011).
Step 2. Next, the residual velocity of the missile after passing through the concrete is estimated using the formula in
NEI 07-13, which is valid for rigid non-deformable missiles with initial velocity less than the perforation velocity.
The ejected concrete plug is assumed to travel at the same
residual velocity as the missile as the two, together, impact
the rear faceplate.
Step 3. The required faceplate thickness, tp, can then be calculated using the formula presented by Børvik et al. (2009).
The corresponding equations for this method are found in
Bruhl et al. (2015a).
Using the three-step method, graphs can be generated for
various missile types or specific wall configurations. Using
the procedure outlined in Bruhl et al. (2015a), Figure 12-2
has been generated for a flat-nosed, 6-in.-diameter, rigid missile impacting walls of any thickness. Similarly, Figure 12-3
has been generated for the minimum practical SC wall—an
interior wall of 12-in.-section thickness, tsc, with 0.25-in.thick faceplates impacted by missiles of various diameters.
For SC walls with 0.015 and 0.050 reinforcement ratios,
respectively, Figures 12-2(a) and (b) provide the required
concrete wall thickness for an initial missile velocity for a
variety of missile weights. Figure 12-3 is used to determine
the capacity of a 12-in.-thick SC wall (minimum permissible
section thickness) for different missile types. If the specified missile to design against—diameter, weight and initial velocity—falls below the applicable line, the wall will
prevent perforation. An increase of 25% in the faceplate
thickness over the value calculated by empirical methods
is necessitated by the scatter in the experimental data. This
scatter, which is essentially independent of empirical equations, is accounted for by a 25% increase in faceplate thickness based on the ASCE Structural Analysis and Design of
Nuclear Plant Facilities Manual (ASCE, 1980).
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(a) 6-in.-diameter, flat-nose, rigid missile, 0.015 reinforcement ratio
(b) 6-in.-diameter, flat-nose, rigid missile, 0.050 reinforcement ratio
Fig. 12-2. Required SC wall thickness to prevent perforation.
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Fig. 12-3. Non-deformable (rigid) missile resistance of minimum SC wall.
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Chapter 13
Fabrication, Erection and Construction Requirements
13.1
DIMENSIONAL TOLERANCES FOR
FABRICATION
(a) SC wall panels and sub-modules fabricated in the
shop and inspected before release.
The dimensional tolerances discussed in ANSI/AISC N690,
Chapter NM, need to be satisfied during the fabrication,
erection and construction of SC panels, sub-modules and
modules. Modular SC construction consists of different
phases. Dimensional tolerances are applicable to:
(b) Adjacent SC walls panels, sub-modules, and modules
just before connecting them.
(c) Erected SC wall modules before concrete casting.
(d) Constructed SC structures after concrete casting.
SC wall panels are typically fabricated in the shop and
then shipped to the field. The overall dimensions of the fabricated SC wall panels are limited by the applicable shipping
restrictions. SC wall panels that are shipped by road are limited to 8 to 12 ft (2.5 to 3.7 m) in width and 40 to 50 ft (12 to
15 m) in maximum length, as shown in Figure 13-1. Additionally, SC wall sub-modules that may consist of corner,
joint or splicing modules may also be fabricated in the shop
and then shipped to the field. They are subjected to the same
size restrictions as the wall panels. There may be additional
height restrictions based on the mode of transportation.
SC wall panels and sub-modules are connected at the site
by welding or bolting to make larger modules, as shown in
Figure 13-2. The size and shape of a module is driven by rigging, handling, and field erection/connection considerations.
These modules are erected and connected to other modules
by welding or bolting to make SC structures, as shown in
Figure 13-3. The tolerances ensure that the faceplates of
empty SC modules are sufficiently aligned and plumb prior
to concrete placement. Concrete is then poured into assembled and erected SC modules and structures.
Fig. 13-1. Phase I: Fabrication of individual
panels with applicable tolerances.
Fig. 13-2. Phase II: Combinations of panels to form a sub-module.
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If the tolerances mentioned in ANSI/AISC N690, Chapter
NM, are met, no additional considerations in analysis need
to be made. Deviations in excess of specified tolerances are
not acceptable, and need to be given due consideration by
performing reconciliatory analysis or by fixing the modules
to meet the tolerances. The dimensional tolerances for SC
wall panels and sub-modules fabricated in the shop have
to be inspected before release for shipping to the site. The
dimensional tolerances are primarily for the fabricated panel
thickness, tsc , where the tolerance at tie locations is equal to
tsc/ 200 rounded up to the nearest z in.(2 mm), and the tolerance between tie locations is equal to tsc/100 rounded up to
the nearest z in. (2 mm).
Due to restricted access within the expanse of the fabricated panels, inspection is required only along the free edges.
Because the fit-up tolerances ensure that panels or submodules can be combined together, measuring these tolerances at the free edges is considered sufficient. Additionally, it is understood that the maximum deviation of SC wall
panels from permissible fit-up tolerances will be at the free
edges. Shipping restrictions limit the maximum width to
10 ft (3 m). Project-specific inspection plans can be developed by the fabricators as needed. The dimensional tolerance
on tie locations is based on the tolerance for steel headed
stud anchor locations in AWS D1.1/D1.1M (AWS, 2010) or
AWS D1.6/D1.6M (AWS, 2007), as applicable. This dimensional tolerance also constrains the tolerances for tie spacing
and the tie angle with respect to the attached faceplates.
The fabricated panels and sub-modules are shipped to
the site and then connected by welding or bolting to make
larger modules. The dimensional tolerances for faceplates
of adjoining panels, sub-modules or modules that are connected by welding are governed by the applicable weld tolerances from the AWS code (AWS D1.1/D1.1M for carbon
steel and AWS D1.6/D1.6M for stainless steel). For welds
that are qualified using project-specific qualification criteria
in AWS, the dimensional tolerances should be based on that
specified in the qualified weld procedure for the project. No
additional squareness or skewed alignment tolerances are
needed except those specified for the faceplates of adjoining
panels, sub-modules or modules.
The dimensional tolerances for the erected SC modules
before concrete placement are based on those for steel structures in the AISC Code of Standard Practice (AISC, 2016a).
The dimensional tolerances for the constructed SC modules
and structures after concrete placement are based on those
for concrete construction in ACI 349-06 (ACI, 2006) and
ACI 117 (ACI, 2010). The faceplate waviness needs to be
checked following concrete placement to limit excessive
faceplate displacement due to concrete placement. ANSI/
AISC N690 Equation NM2.1 provides the waviness requirement. Figure 13-4 illustrates how faceplate waviness is measured. The faceplate waviness discussed refers to the total
out-of-straightness of the faceplates and is not the net difference between waviness before and after concrete hardening. Corrective measures or reconciliatory analysis need to
be performed in case the faceplate waviness requirement is
not met.
Fig. 13-3. Phase III: Erection of a module at the site prior to concreting.
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Benchmarked finite element models (Zhang et al., 2014)
were used to study the effect of faceplate waviness on the
compressive strength of SC walls with nonslender and slender faceplates. Finite element models of nonslender SC walls
with faceplate waviness up to 0.65tp were analyzed. The
faceplates developed more than 95% of their yield strength,
0.95AsFy, at the axial compressive strength. Figure 13-5 was
developed using the results of the finite element analyses. It
illustrates the compression force, Fsteel, carried by the faceplates normalized with respect to its yield strength, AsFy,
versus the average strain over the length. For nonslender
faceplates, s/tp = 24, the reduction in the normalized compressive strength of the faceplates is less than 5% for an
increase in imperfection from 0.1tp to 0.6tp. However, for
slender faceplates, s/tp = 36, that are not permitted by ANSI/
AISC N690 Appendix N9, this reduction in the normalized
compressive strength is more substantial, and the post-peak
behavior is degrading. Bhardwaj and Varma (2016) observed
that SC walls meeting the faceplate waviness requirement
and the detailing requirements of Appendix N9 that shear
reinforcement is spaced at tsc/2, do not experience significant loss in available compressive strength due to initial
imperfections and concrete casting pressure when considering a typical pour height of 10 ft. However, the effects of
imperfections need to be considered when the concrete pour
height is larger or the ties are spaced at the section thickness.
Fig. 13-4. Faceplate waviness—the faceplate waviness and the variation
in tie dimensions have been exaggerated for illustration purposes.
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Fig. 13-5. Normalized force carried by faceplates versus average strain.
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Chapter 14
Quality Assurance and Quality Control Requirements
The construction of SC walls needs to meet the quality assurance (QA) and quality control (QC) requirements provided
in ANSI/AISC N690, Chapter NN. This section requires
inspections to be performed for faceplates and installation of
ties and steel anchors before concrete placement. After the
concrete placement, the steel faceplates need to be inspected
for waviness. The acceptance or rejection of the elements
needs to be documented.
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Appendix A: Design Example
Given:
Verify the design of a sample SC wall using the provisions of ANSI/AISC N690 Appendix N9 (AISC, 2015). For the purpose of
this calculation, realistic SC wall details are considered. Use ASTM A572 Grade 50 steel for the faceplates and the ties. Assume
that the ties act as the shear reinforcement for this SC wall and that the ties are connected to the SC walls by complete-jointpenetration (CJP) groove welds. Use normal weight concrete with wc = 145 lb/ft3 and a compressive strength of ƒ′c = 5 ksi.
The procedure followed in this calculation is consistent with that outlined in ANSI/AISC N690 Appendix N9, Figure C-AN9.1.1. Unless mentioned otherwise, the sections mentioned in the calculation correspond to ANSI/AISC N690. The symbols
and units used are consistent with ANSI/AISC N690.
The calculation can be organized into the following steps:
Step 0. Preliminary details of SC walls
Step 1. Minimum Appendix N9 applicability requirements
Step 2. Faceplate slenderness requirement
Step 3. Shear connector detailing
Step 4. Tie detailing
Step 5. Stiffness and other parameters for modeling SC walls
Step 6. Analysis results and required strength summary
Step 7. Individual design available strengths
Step 8. Interaction of design available strengths
Step 9. Demand capacity ratios and interaction surfaces
Step 10. Demands for anchorage design
Step 11. Impactive and impulsive loading
Step 12. Design of SC wall connections
Step 13. Combination of demands
Step 14. Connection detailing
Step 15. Design optimization
Note: The calculation does not consider any penetrations in the SC wall. The calculation uses U.S. customary units. Calculations
can also be performed using SI units, with corresponding equations and parameter values provided in ANSI/AISC N690 Appendix N9. Because the demands are calculated for LRFD load combinations, the demand capacity ratio checks have been performed
using LRFD. ASD calculations can be performed if the demands are obtained for ASD load combinations.
Solution
From AISC Manual Table 2-4, the material properties are as follows:
Faceplates:
ASTM A572 Grade 50
Fy = 50 ksi
Fu = 65 ksi
Ties:
ASTM A572 Grade 50
Fy.tie = 50 ksi
Fu.tie = 65 ksi
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Steel properties are as follows:
Es = 29,000 ksi
G = 11,200 ksi
From AISC Specification Appendix 4:
αs = thermal expansion coefficient of steel
= 7.8 × 10−6/ °F for temperature > 150°F
From the AISC Steel Construction Manual Table 17-12 for rolled steel:
γs = density of steel
= 490 lb/ft3
From Appendix N9, Section N9.2.2, concrete properties are as follows:
Ec = ( wc )1.5
fc′
1.5
= (145 lb/ft 3 )
5 ksi
= 3,900 ksi
Gc = 772 fc′
= 772 5 ksi
= 1, 730 ksi
From Hong and Varma (2009):
cc = speciÿc heat
Btu
= 255.4
lb × Δ°F
υc = 0.17
From CEN (2009):
kc = thermal conductivity
Btu
= 0.013
ft × sec × Δ°F
(Eurocode Eq. 4)
From ACI (2008):
αc = thermal expansion coefficient
= 5.6 × 10 −6/ °F for temperature = 392°F
Step 0. Preliminary Details of SC Walls
The SC wall details assumed to begin with are based on typical plant layout details provided to the structural engineers at the
beginning of the process. Plant layout engineers and designers often select the wall thickness and other parameters based on
shielding requirements and past practice. During the plant layout design phase, structural engineers recommend standard steel
ratios and section details to be simple and consistent. During the detailed design stage, the structural engineer’s job is to check,
design and finalize the SC wall details.
The critical section of the wall is selected from a portion of the refueling cavity, in the elevation range between the operating floor
slabs at top-of-concrete elevations 40 ft and 66 ft. For this calculation, the following parameters are used:
hwall = unsupported height of SC wall
= 66.0 ft − 40.0 ft
= 26.0 ft
tsc
= SC section thickness
= 56.0 in.
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tp
= faceplate thickness
= 0.500 in.
s
= shear connector spacing
= 6.00 in.
stt
= shear reinforcement transverse spacing
= 24.0 in.
stl
= shear reinforcement longitudinal spacing
= stt
= 24.0 in.
Steel headed stud anchors with a diameter, ds, of w in. are used as shear connectors and flat bars, 0.5 in. × 6 in., are used as tie
bars.
Atie = ts ls
= (0.500 in.)(6.00 in.)
= 3.00 in.2
Fu.sc = 65 ksi
ds
= 0.750 in.
ls
= 6.00 in.
Thermal conditions are as follows:
Ambient temperature
Tamb = 70°F
Operating temperature
Top = 120°F
All calculations are performed for a unit width of the wall, l = 12.0 in./ft
Step 1. Minimum Appendix N9 Applicability Requirements
For the provisions of ANSI/AISC N690 Appendix N9 to be applicable, the SC wall needs to satisfy the general provisions of Section N9.1.1. This step of the calculation verifies that the SC wall being considered meets these requirements. The requirements
are checked in the same order they appear in Section N9.1.1. If a provision is not satisfactorily met, the wall parameters will be
updated to satisfy these requirements.
(a) SC section thickness, tsc
Requirement: 18 in. ≤ tsc ≤ 60 in. for exterior SC walls
tsc = 56.0
Therefore, the SC section thickness considered is permitted.
(b) Faceplate thickness, tp
Requirement: 0.25 in. ≤ tp ≤ 1.5 in.
tp = 0.500 in.
Therefore, the SC faceplate thickness considered is permitted.
(c) Reinforcement ratio, ρ
Requirement: 0.015 ≤ ρ ≤ 0.050
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2 tp
tsc
2 ( 0.500 in.)
=
56.0 in.
= 0.018
ρ=
(N690 Eq. A-N9-1)
Therefore, the reinforcement ratio considered is permitted.
(d) Specified minimum yield stress of faceplates, Fy
Requirement: 50 ksi ≤ Fy ≤ 65 ksi
Fy = 50 ksi
Therefore, the specified minimum yield stress of faceplates considered is permitted.
(e) Specified minimum concrete compressive strength, ƒ′c
Requirement:
4 ksi ≤ ƒ′c ≤ 8 ksi; lightweight concrete is not permitted
ƒ′c = 5 ksi; normal weight concrete is used
Therefore, the specified minimum concrete compressive strength considered is permitted. Also, lightweight concrete is not
used.
(f)Check that the faceplate is nonslender
This requirement will be checked in Step 2 of the calculation. In case the requirement is not met, the shear connector or shear
reinforcement spacing will be adjusted.
(g)Ensure composite action between faceplates and concrete using shear connectors
The development of composite action will be verified in Step 3. In case the requirement is not met, the shear connector spacing will be adjusted.
(h)Ensure tie requirements are met
The tie requirements are checked in Step 4. If required, the tie spacing and area will be updated to satisfy the requirements.
(i)Ensure ductile failure of faceplates with holes
Because the SC wall considered does not have any holes, this requirement does not need to be checked.
(j)Nominal faceplate thickness, tp, and yield stress, Fy, is required to be the same for both faceplates
Both faceplates have the same nominal thickness and yield stress; therefore, this requirement is satisfied.
(k)Steel rib embedment and welds
Steel ribs are not used in this example, and therefore the embedment and weld requirements for ribs are not discussed here.
(l)Splices between faceplates
The region of SC wall considered does not have any splices. Therefore, the splice connection strength requirements are not
checked.
Step 2. Faceplate Slenderness Requirement
The faceplates are required to be nonslender according to ANSI/AISC N690, Section N9.1.3.
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b
E
≤ 1.0 s
tp
Fy
(N690 Eq. A-N9-2)
b = min (s, stt, stl )
s = 6.00 in.
stt = 24.0 in.
stl = 24.0 in.
b = 6.00 in.
The value of b is calculated for the arrangement of shear connectors and ties shown in Figure A-1. For different arrangements, b
may have to be calculated differently. The tie bars and steel headed stud anchors contributing to the unit cell shown are used to
avg value in Step 8a of this example.
calculate the Qcv
b
6.00
=
tp 0.500
= 12.0
Fig. A-1. Arrangement of shear connectors and ties.
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1.0
Es
Fy
= 1.0
29, 000 ksi
50 ksi
= 24.0
b
= 12.0 < 24.0
tp
Therefore, the faceplate slenderness requirement is satisfied.
Step 3. Shear Connector Detailing
The detailing of shear connectors needs to be checked to meet the requirements of ANSI/AISC N690, Section N9.1.4. These
requirements ensure the composite action of SC walls.
(a) Classification of steel anchors
According to Section N9.1.4a, steel headed stud anchors are yielding shear connectors. In case any other type of steel
anchors are used, the classification and available strength, Qcv , need to be established through testing.
(b) Spacing of steel anchors
According to Section N9.1.4b, the spacing of steel anchors need not exceed the following:
(1) Spacing, s, required to develop the yield strength of the faceplates over the development length, Ld
s ≤ c1
Qcv Ld
Tp (N6901 Eq. A-N9-3)
where
L d = development length, in.
≤ 3tsc
= 3(56.0 in.)
= 168 in.
Qcv = available shear strength of steel anchor, kips
= ϕvQnv
= ϕvFu.sc Asa
(from Spec. Eq. I8-3)
and where
π
Asa = d s2
4
2
π
= ( 0.750 in.)
4
= 0.442 in.2
ϕv = 0.65
and then
Qcv = 0.65(65 ksi)(0.442 in.2)
= 1.87 kips
Tp = faceplate tensile strength per unit width, kip/in.
= Fy tp
= (50 ksi)(0.500 in.)
= 25.0 kip/in.
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c1 = factor used to determine spacing of steel anchors
= 1.0 for yielding steel anchors
c1
Qcv Ld
(18.7 kips)(168 in.)
= 1.0
25.0 kip/in.
Tp
= 11.2
(from N690 Eq. A-N9-3)
s = 6.00 in. < 11.2 in.
Therefore, the spacing requirement based on the development length is satisfied.
(2) Spacing required to prevent interfacial shear failure before out-of-plane shear failure
s ≤ c1
Qcv l
Vc 0.9tsc (N690 Eq. A-N9-4)
The value of available out-of-plane shear strength of the SC wall is needed to check this requirement. Because this
requirement will typically not govern, it will not be checked at this point. It will be checked after available strengths
have been calculated in Step 7.
(3) Requirements of AISC Specification Sections I8.1 and I8.3e
(i) Diameter of the stud:
ds ≤ 2.5tp
0.750 in. ≤ 2.5 (0.500 in.)
0.750 in. < 1.25 in. o.k.
(ii) Spacing requirements according to Section I8.3e:
s ≥ 4ds
6.00 in. ≥ 4(0.750 in.)
6.00 in. > 3.00 in. o.k.
s ≤ 32ds
6.00 in. ≤ 32(0.750 in.)
6.00 in. < 24.0 in. o.k.
Therefore, the steel headed stud anchor requirements of the AISC Specification are satisfied.
Step 4. Tie Detailing
Ties provide structural integrity to the SC wall. Tie bar requirements of ANSI/AISC N690, Section N9.1.5, need to be satisfied.
(a)Tie bar spacing
ANSI/AISC N690 requires the tie bar spacing to be less than or equal to the section thickness, tsc.
stt ≤ tsc
stl ≤ tsc
stt = 24.0 in. < tsc = 56.0 in.
stl = 24.0 in. < tsc = 56.0 in.
Therefore, the spacing requirement is satisfied.
(b)Classification of ties
Ties are to be classified as yielding or nonyielding shear reinforcement based on the provisions of ANSI/AISC Section
N9.1.5a.
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Ties are classified as yielding shear reinforcement when:
Fny ≤ 0.8Fnr
(N690 Eq. A-N9-5)
where
Fnr = nominal rupture strength of the tie, kips
= Fu.tie Atie
= (65 ksi)(3.00 in.2 )
= 195 kips
Fny = nominal yield strength of the tie, kips
= Fy.tie Atie
= (50 ksi)(3.00 in.2 )
= 150 kips
Fny ≤ 0.8Fnr
150 kips ≤ 0.8 (195 kips)
150 kips < 156 kips
Because the tie bars are connected to faceplates using complete-joint-penetration groove welds, the nominal strength of the
connection will be equal to or greater than the member strength.
Therefore, the reinforcement is classified as yielding shear reinforcement.
(c)Required tensile strength of ties
The required tensile strength for individual ties, Freq, is:
t p Fy tsc ⎞ ⎛ stt ⎞ ⎡
6
⎤
Freq = ⎛⎜
⎝ 4 ⎟⎠ ⎜⎝ stl ⎟⎠ ⎢ ⎛ tsc ⎞ 2 ⎥
⎢ 18 ⎜ ⎟ + 1 ⎥
⎢⎣ ⎝ stl ⎠
⎥⎦
(N690 Eq. A-N9-6)
6
⎡ ( 0.500 in.)( 50 ksi )( 56.0 in.) ⎤ ⎛ 24.0 in. ⎞ ⎡
⎤
=⎢
2
⎥
⎢
⎥
⎝
⎠
4
56.0 in. ⎞
⎦ 24.0 in.
⎣
+ 1⎥
⎢ 18 ⎛
⎣ ⎝ 24.0 in. ⎠
⎦
= 21.2 kips
The available tensile strength of a tie should be greater than the required strength.
From AISC Specification Section J4.1(a), the available yield strength of the ties is:
ϕt.y = 0.90
ϕt.y Fny = 0.90 (150 kips)
= 135 kips
From AISC Specification Section J4.1(b), the available rupture strength of the tie is:
ϕt.r = 0.75
ϕt.r Fnr = 0.75 (195 kips)
= 146 kips
min (ϕt.y Fny, ϕt.r Fnr) = 135 kips ≥ Freq = 21.2 kips
Therefore, the ties meet the tensile strength requirements. The ties also contribute to the out-of-plane shear strength of SC
walls. The contribution of ties will be considered when available strengths are calculated in Step 7.
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Step 5. Stiffness and Other Parameters for Modeling SC Walls
A three-dimensional elastic finite element model of the structure comprised of SC walls is analyzed in commercial finite element
software. The walls are modeled according to ANSI/AISC N690, Sections N9.2.1 and N9.2.3.
(a) General Provisions—Section N9.2.1
(1) A three-dimensional SC wall is analyzed using elastic, thick-shell finite elements.
(2) Second-order effects
As discussed in ANSI/AISC N690, Section N9.1.2b, if provisions of ACI 318, Section 6.2.5, are met, second-order
effects need not be considered. Because the SC walls are braced at floor levels, ACI 318, Equation 6.2.5b is considered:
klu
≤ 34 − 12 ( M1 / M 2 ) ≤ 40
r
(ACI 318 Eq. 6.2.5b)
where
k = effective length factor
lu = unsupported length of compression member, in.
r = radius of gyration, in.
Based on the recommendations in ACI 318, Section 10.10.1:
k = 1.0
r = 0.3tsc
= 0.3(56.0 in.)
= 16.8 in.
Also, conservatively consider single curvature and M1/ M2 = 1.0.
Solving Equation 10-7 for lu , the largest unsupported height permitted is:
⎡34 − (12 ) ( M1 / M 2 ) ⎤⎦ r
lu = ⎣
k
[34 − (12)(1.0 )](16.8 in.)
=
1.0 (12 in./ft )
= 30.8 ft
hwall = actual wall height
= 26 ft
hwall ≤ lu
Because the actual wall height is less than the largest unsupported height permitted, second-order effects do not need
to be considered.
(3) Analysis for accident thermal loads has been conducted as required by ANSI/AISC N690, Section N9.2.4. The loads
from accident thermal conditions are linearly superimposed on other loads (condition B load combinations). This is
explained in more detail in Step 6, where analysis results are presented.
(4) For safe shutdown earthquake seismic analysis, a viscous damping ratio of 5% is assumed.
(b)Stiffness for analysis
The stiffness for analysis is calculated according to ANSI/AISC N690, Section N9.2.2. Different stiffness values are needed
for operating thermal (Condition A) and accident thermal (Condition B).
(1) Effective flexural stiffness for analysis, EIeff
The effective flexural stiffness is determined for the operating thermal condition and for the accident thermal condition
using ANSI/AISC N690, Equation A-N9-8:
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⎛ ΔTsavg ⎞
EI eff = ( Es I s + c2 Ec I c ) ⎜ 1 −
⎟ ≥ Es I s
⎝
150 ⎠
(N690 Eq. A-N9-8)
where
I c = moment of inertia of concrete infill per unit width, in.4 /ft
=
ltc3
12
and where
tc = thickness of concrete infill, in.
= tsc − 2tp
= 56.0 in. − 2(0.500 in.)
= 55.0 in.
Ic =
(12 in./ft )( 55.0 in.)3
12
= 166,000 in.4 /ft
I s = moment of inertia of faceplates per unit width, in.4 /ft
lt p (tsc − t p )2
2
(12 in./ft )( 0.500 in.)( 56.0 in. − 0.500 in.)2
=
2
= 9, 240 in.4 /ft
=
c2 = calibration constant for determining effective flexural stiffness
= 0.48ρ′ + 0.10
and where
ρ′ = stiffness adjusted modular ration
= ρn
n = modular ratio of steel to concrete
E
= s
Ec
29,000 ksi
=
3,900 ksi
= 7.44
ρ′ = 0.018(7.44)
= 0.134
c2 = 0.48(0.134) + 0.10
= 0.164
(i) Operating thermal condition (Condition A)
Using ANSI/AISC N690, Equation A-N9-8, shown previously with ΔTsavg = 0 based on the User Note in Section
N9.2.2(a):
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ΔTsavg ⎞
⎛
EI eff = ( Es I s + c2 E3 I c ) ⎜ 1 −
⎟ ≥ Es I s
⎝
150 ⎠
(N690 Eq. A-N9-8)
0 ⎞
= ⎡⎣( 29,000 ksi ) ( 9, 240 in.4 /ft ) + 0.164 ( 3,900 ksi ) (166,000 in.4 /ft ) ⎤⎦ ⎛ 1 −
⎝ 150 ⎠
= 3.74 × 108 kip-in.2 /ft
Es I s = ( 29,000 ksi ) ( 9, 240 in. /ft )
4
= 2.68 × 108 kip-in.2 /ft
ΔTsavg ⎞
⎡
⎤
⎛
EI eff .op = max ⎢( Es I s + c2 Ec I c ) ⎜ 1 −
⎟ , Es I s ⎥
⎝
150 ⎠
⎣
⎦
= 3.74 × 108 kip-in.2 /ft
(ii) Accident thermal condition (Condition B)
Accident thermal loading is obtained from heat transfer analysis, as discussed in ANSI/AISC N690, Section N9.2.4.
It is explained in detail in Section 7.5. Heat transfer analysis results are not presented in this example.
ΔTsavg = 190Δ°F
(from heat transfer analysis)
ΔTsavg ⎞
⎛
EI eff = (Es I s + c2 Ec I c ) ⎜ 1 −
⎟ ≥ Es I s
⎝
150 ⎠
(N690 Eq. A-N9-8)
190 ⎞
= ⎡⎣( 29,000 ksi ) ( 9, 240 in.4 /ft ) + 0.164 ( 3,900 ksi ) (166,000 in.4 /ft ) ⎤⎦ ⎛ 1 −
⎝ 150 ⎠
= −9.99 × 10 7 kip-in.2 /ft
Es I s = ( 29,000 ksi ) ( 9, 240 in. /ft )
4
= 2.68 × 108 kip-in.2 /ft
ΔTsavg ⎞
⎡
⎤
⎛
, Es I s ⎥
EI eff . acc = max ⎢( Es I s + c2 Ec I c ) ⎜ 1 −
⎟
⎝
150 ⎠
⎣
⎦
= 2.68 × 108 kip-in.2 /ft
(2) Effective in-plane shear stiffness per unit width, GAeff
According to ANSI/AISC N690, Section N9.2.2(b), to use the provisions of this Appendix, the value of the average inplane shear demand for the wall, Srxy, relative to the concrete cracking threshold, Scr, needs to be known. However, this
is not possible before the analysis is done.
To proceed with the analysis, it is assumed that the average in-plane shear demand is 1.5 times the concrete cracking
threshold for Condition A analysis. This assumption will be verified after the demands are obtained from the analysis
in Step 6.
⎛ GAuncr − GA cr ⎞
GAeff = GAuncr − ⎜
⎟⎠ (Srxy.as − Scr )
⎝
Scr
(from N690 Eq. A-N9-11)
where
GAcr = 0.5 ( ρ )
− 0.42
GAs
(N690 Eq. A-N9-12)
and where
As = 2ltp
= 2 (12 in./ft )( 0.500 in.)
= 12.0 in.2 /ft
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ρ
=
As Fy
31.6 Ac f c′ (N690 Eq. A-N9-13)
and where
Ac = area of concrete infill per unit width, in.2/ft
= ltc
= (12.0 in./ft)(55.0 in.)
= 660 in.2/ft
(12.0 in.2 /ft ) ( 50 ksi )
ρ =
31.6 ( 660 in.2 /ft ) 5 ksi
= 0.0129
Therefore:
GAcr = 0.5(0.0129)−0.42(11,200 ksi)(12 in.2/ft)
= 418,000 kip/ft
GAeff = GAuncr
= GAs + Gc Ac
= (11,200 ksi)(12.0 in.2/ft) + (1,730 ksi)(660 in.2/ft)
= 1.28 × 106 kip/ft
(N690 Eq. A-N9-9)
Scr = concrete cracking threshold, kip/ft
=
0.063 fc′
GAuncr
Gc
(N690 Eq. A-N9-10)
0.063 5 ksi
(1.28 × 106 kip/ft )
1,730 ksi
= 104 kip/ft
Because Srxy is assumed to be 1.5Scr:
=
Srxy.as = 1.5Scr
= 1.5(104 kip/ft)
= 156 kip/ft
⎡ (1.28 × 106 kip/ft ) − ( 4.18 × 105 kip/ft ) ⎤
⎥ (156 kip/ft − 104 kip/ft )
GAeff = (1.28 × 10 6 kip/ft ) − ⎢
104 kip/ft
⎢⎣
⎥⎦
= 849,000 kip/ft
(3) For accident thermal load conditions (Condition B in Step 6), GAeff is taken as GAcr.
(4) The SC wall connection-to-basemat is considered rigid for out-of-plane moment demands and is modeled as a rigid
connection.
(c) Geometric and material properties for elastic finite element analysis
The geometric and material properties used for elastic finite element analysis are consistent with ANSI/AISC N690, Section
N9.2.3.
(1) For the following properties, concrete values are used for the finite elements:
Poisson’s ratio
υm = υc
= 0.17
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Thermal expansion coefficient
αm = αc
= 5.6 × 10−6/ °F
Thermal conductivity
k m = kc
= 0.01
Btu
ft × sec × Δ°F
(2) Model elastic modulus, Em , and model thickness, tm
These parameters for the finite element model are obtained by calibrating the effective flexural and shear stiffnesses.
The flexural and shear stiffnesses of the model are equated with the corresponding effective stiffnesses determined in
Step 5(b):
ltm3
= EI eff
12
Em
ltm = GAeff
2 (1 + υm )
Em
These equations are solved to obtain tm and Em as follows:
(i) For operating thermal conditions (Condition A)
⎛ EI eff .op ⎞ ⎡ 12
⎤
tm.op = ⎜
⎢ 2 (1 + υ ) ⎥
⎟
GA
⎝
eff ⎠ ⎣
m ⎦
(A-1)
⎛ 3.74 × 108 kip-in.2 /ft ⎞ ⎡
⎤
12
= ⎜
⎢ 2 (1 + 0.17 ) ⎥
⎟
849,000
kip/ft
⎝
⎠⎣
⎦
= 47.5 in.
Em.op =
=
GAeff 2 (1 + υm )
tm.opl
(A-2)
(849,000 kip/ft ) ( 2)(1 + 0.17)
( 47.5 in.)(12 in./ft )
= 3, 490 ksi
(ii) For accident thermal conditions (Condition B)
⎛ EI eff .acc ⎞ ⎡ 12
⎤
tm.acc = ⎜
⎢
⎥
⎟
⎝ GAeff ⎠ ⎣ 2 (1 + υm ) ⎦
(A-3)
⎛ 2.68 × 108 kip-in.2 /ft ⎞ ⎡
⎤
12
= ⎜
⎥
⎢
⎟
⎝ 849,000 kip/ft ⎠ ⎣ 2 (1 + 0.17 ) ⎦
= 40.2 in.
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Em.acc =
=
GAeff 2 (1 + υ m )
tm.acc l
(A-4)
(849,000 kip/ft ) ( 2)(1 + 0.17)
( 40.2 in.) (12 in./ft )
= 4,120 ksi
(3) Material density, γm
(i) For operating thermal conditions (Condition A)
γ s ( 2t p ) + wc tc
γ m.op =
(A-5)
tm.op
( 490 lb/ft 3 ) ( 2 )( 0.500 in.) + (145 lb/ft 3 ) ( 55.0 in.)
=
47.5 in.
= 178 lb/ft
3
(ii) For accident thermal conditions (Condition B)
γ m.acc =
=
γ s ( 2 t p ) + wc tc
(A-6)
tm.acc
( 490 lb/ft 3 ) ( 2 )( 0.500 in.) + (145 lb/ft 3 ) ( 55.0 in.)
40.2 in.
= 186 lb/ft
3
(4) Specific heat, cm
Specific heat is the same for both operating and accident thermal conditions.
cm =
=
cc wc tc
γ m.optm.op
(A-7)
Btu ⎞
⎛ 255.4
(145 lb/ft 3 ) ( 55.0 in.)
⎝
lb × Δ°F ⎠
= 241
(178 lb/ft 3 ) ( 47.5 in.)
Btu
lb × Δ°F
(d) Analysis involving accident thermal conditions (Condition B)
Heat transfer analysis is performed for accident loading. The results of this analysis serve as input for the structural analysis.
The analysis is conducted using the geometric and material properties defined. Temperature histories and through-thickness
temperature profiles obtained from heat transfer analysis are used in the structural analysis. This design example does not
discuss the heat transfer analysis results. Because the thermal loads are applied as a uniform temperature increase through
the wall, a thermal gradient out-of-plane moment needs to be added to the out-of-plane demands. The magnitude of moment
considered is determined in the following.
The maximum temperature difference between faceplates due to accident thermal conditions, obtained from the accident
data, is:
ΔTsg = 28.5 Δ°F
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Table A-1. Load Combinations for Analysis
S. No.
Load Combination
ANSI/AISC N690 Equation
1
1.4(D + Ro + F) + To + C
NB2-1
2
1.2(D + Ro + F) + 1.6(L + H) + 0.5(Lr or R or S) + 1.2To + 1.4C
NB2-2
3
1.2(D + Ro + F) + 0.8(L + H) + 1.6(Lr or R or S) + 1.2To + 1.4C
NB2-3
4
1.2(D + Ro + F) + W + 0.8L + 1.6H + 0.5(Lr or R or S) + To + C
NB2-4
5
1.2(D + Ro + F) + W + 0.8L + 1.6H + 0.5(Lr or R or S) + To + C
NB2-4
6
1.2(D + Ro + F) + 1.6Eo + 0.8L + 1.6H + 0.2(Lr or R or S) + To + C
NB2-5
7
1.2(D + Ro + F) + 1.6Eo + 0.8L + 1.6H + 0.2(Lr or R or S) + To + C
NB2-5
8
D + 0.8L + C + To + Ro + Es + F + H
NB2-6
9
D + 0.8L + C + To + Ro − Es + F + H
NB2-6
10
D + 0.8L + To + Ro + Wt + F + H
NB2-7
11
D + 0.8L + To + Ro − Wt + F + H
NB2-7
12
D + 0.8L + C + 1.2Pa + Ra + Ta + F + H
NB2-8
13
D + 0.8L + Pa + Ra + Ta + Yr + Yj + Ym + 0.7Es + F + H
NB2-9
14
D + 0.8L + Pa + Ra + Ta + Yr + Yj + Ym − 0.7Es + F + H
NB2-9
⎛ α s ΔTsg ⎞
M r -th = EI e ff.acc ⎜
⎝ tsc ⎟⎠
(from N690 Eq. A-N9-14)
⎡ ( 7.8 × 10 −6/ °F )( 28.5°F )⎤
⎥
= ( 2.68 × 10 kip-in. /ft ) ⎢
56.0 in.
⎢⎣
⎥⎦
= 1, 060 kip-in./ft
8
2
Note: This limit is not applicable to connection regions. The out-of-plane thermal moment will be determined from finite
element analysis.
Step 6. Analysis Results and Required Strength Summary
The expanse of the wall considered is 44 ft × 26 ft. Thick shell finite elements are used. The material properties discussed in
Step 5 are used. The element size is 2 ft × 2 ft. The wall is modelled using 120 elements. Load combinations for analysis are
based on ANSI/AISC N690, Chapter NB. Table A-1 presents the load combinations considered.
As discussed earlier, two sets of analyses are performed. Load combinations 1 through 11 use analysis results based on condition A (operating thermal). Load combinations 12 through 14 use analysis results for condition B (accident thermal). The finite
element analysis data for each element and load combination is combined and studied. The database consists of element number,
load combination and associated demands for each element. The demands are measured per unit width.
For this design example, the whole data set is not presented. Data for only the elements with the highest individual demands is
presented in Table A-2. The highest magnitude required strength of each individual demand has been boldfaced. The out-of-plane
moment due to accident thermal gradient calculated from ANSI/AISC N690, Equation A-N9-14, has been added to the moment
demands obtained from finite element analysis. The nomenclature for required strengths is based on ANSI/AISC N690, Section
N9.2.5. Consistent with the design practice, the required strengths for each element are compared with the available strengths. In
case the demand is greater than the available strength, the required strengths are permitted to be averaged as discussed in ANSI/
AISC N690, Section N9.2.5.
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Table A-2. Peak Demands for Elements
Element
No.
Load
Comb.
Srx
(kip/ft)
Sry
(kip/ft)
Srxy
(kip/ft)
Mrx
(kip-in./ft)
Mry
(kip-in./ft)
Mrxy
(kip-in./ft)
Vrx
(kip/ft)
Vry
(kip/ft)
54664
9
−105
−237
−88.4
−1400
−2320
−364
−14
−58.4
54664
8
59.7
146
54692
8
262
26.6
261
1680
2520
528
16.2
50.3
37.0
1160
1810
165
28.7
33.2
54664
8*
93.5
160
258
1900
3070
559
13.8
54.1
54692
13
193
−75.1
−67.6
4300
6350
223
61.5
123
54664
12
−369
342
215
2350
7000
540
16.7
107
39007
13
−237
159
7640
3600
39001
14
−350
−137
−307
−2660
−2110
−1250
−5.18
−30.2
−48.2
−31.2
54664
14
−444
−57.9
−143
−3990
−3250
−500
-4.67
−40.1
Condition A
Condition B
60.0
−58.1
*Includes reaction and pressure loads.
For the design of the SC wall section, demand capacity ratios for each element are checked for all the load combinations. This is
done for individual as well as combined demands.
The average in-plane shear demand, Srxy, for a particular operating thermal (Condition A) load combination is determined by
averaging the in-plane shear demands of all the elements for that load combination. It is observed that the maximum average
in-plane shear demands occur for load combinations 8 and 9. Figure A-2 presents the ratio of in-plane shear demand and concrete cracking threshold for each element for load combination 9. The average ratio for all elements is around 1.5. The average
demand is close to the assumption of 1.5Scr for determining the in-plane shear stiffness that was used in Step 5(b), and therefore the assumption is valid. However, there may be cases where the average in-plane shear demand is not in the range of the
value assumed to ascertain shear stiffness. In that case, the process of calculating shear stiffness and the analysis will need to be
repeated.
Step 7. Individual Design Available Strengths
The available strengths of the SC wall section for individual demand types are determined based on ANSI/AISC N690, Section
N9.3.
(a) Uniaxial tensile strength
The available uniaxial tensile strength is determined according to the provisions of AISC Specification Chapter D. Because
no holes are present in the expanse of the SC wall being designed, the rupture strength need not be greater than the yield
strength. Here the contribution of the concrete is ignored.
The available tensile strength is determined as the lesser of the tensile yielding strength or the tensile rupture strength.
For tensile yielding:
ϕPn.ten = ϕt.yFyAg
(from Spec. Eq. D2-1)
where
Ag = (2tp)(l)
= 2(0.500 in.)(12 in./ft)
= 12.0 in.2/ft
ϕ t.y = 0.90
And thus:
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Pn.ten = Fy Ag
= (50 ksi)(12 in.2/ft)
= 600 kip/ft
ϕPn.ten = (0.90)(600 kip/ft)
= 540 kip/ft governs
For tensile rupture:
ϕPn.ten = ϕt.rFuAg
(from Spec. Eq. D2-2)
where
ϕ t.r = 0.75
And thus:
Pn.ten = Fu Ag
= (65 ksi)(12 in.2/ft)
= 780 kip/ft
ϕPn.ten = (0.75)(780 kip/ft)
= 585 kip/ft
The available tensile strength of the SC wall is
ϕPn.ten = 540 kip/ft
(b)Compressive strength
The available compressive strength of the SC wall section is determined using AISC Specification Section I2.1b, with the
faceplates taking the place of the steel shape.
/
Fig. A-2. Srxy Scr ratio for load combination 9.
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The ratio of the nominal compressive strength of zero length, Pno, to the elastic critical buckling load, Pe, must first be determined in order to ascertain which equation for the nominal compressive strength, Pn, will control.
Pe =
π 2 EI ef f.buck
L2
Pno = Fy Asn + 0.85ƒ′c Ac
(from N690 Eq. A-N9-16)
(N690 Eq. A-N9-15)
where
Asn
= net area of faceplates per unit width, in.2/ft
= As
= 12.0 in.2/ft
EIeff.buck = EsIs + 0.60EcIc
= (29,000 ksi)(9,240 in.4/ft) + 0.60(3,900 ksi)(166,000 in.4/ft)
= 6.56 × 108 kip-in.2/ft
L
= hwall
= (26.0 ft)(12 in./ft)
= 312 in.
(from N690 Eq. A-N9-17)
Pe and Pno can then be calculated:
Pe =
=
π 2 EI ef f.buck
L2
(from Spec. Eq. I2-5)
π 2 ( 6.56 × 108 kip-in.2 /ft )
( 312 in.)2
= 66,500 kip/ft
Pno = Fy As + 0.85ƒ′c Ac
= (50 ksi)(12.0 in.2/ft) + 0.85(5 ksi)(660 in.2/ft)
= 3,410 kip/ft
(from Spec. Eq. I2-4)
3, 410 kip/ft
Pno
=
Pe 66,500 kip/ft
= 0.0513
Because
Pno
< 2.25 :
Pe
Pno
⎛
⎞
Pn.com = Pno ⎜ 0.658 Pe ⎟
⎝
⎠
(from Spec. Eq. I2-2)
= ( 3, 410 kip/ft ) ( 0.6580.0513 )
= 3,340 kip/ft
From AISC Specification Section I2.1b:
ϕc = 0.75
ϕPn.com = ϕc Pn.com
= (0.75)(3,340 kip/ft)
= 2,510 kip/ft
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(c)Out-of-plane flexural strength
The nominal flexural strength per unit width of the SC wall is determined for the limit state of yielding using AISC N690,
Section N9.3.3:
Mn = Fy AsF(0.9tsc)
(N690 Eq. A-N9-18)
ϕb = 0.90
where
AsF = gross cross-sectional area of faceplate in tension due to flexure per unit width, in.2 /ft
As
2
12.0 in.2 /ft
=
2
= 6.00 in.2 /ft
=
Mn = Fy AsF(0.9tsc)
= (50 ksi)(6.00 in.2/ft)(0.9)(56.0 in.)
= 15,100 kip-in./ft
ϕMn = ϕbMn
= (0.90)(15,100 kip-in./ft)
= 13,600 kip-in./ft
(d)In-plane shear strength
The design in-plane shear strength of the SC wall per unit width, ϕviVni, is determined for the limit state of yielding of the
faceplates using ANSI/AISC N690, Section N9.3.4:
Vni = κFy As
(N690 Eq. A-N9-19)
ϕvi = 0.90
where
= 1.11 − 5.16ρ ≤ 1.0
= 1.11 − 5.16(0.013)
= 1.04 > 1.0 → therefore κ = 1.0
Vni = κFy As
= (1.0)(50 ksi)(12.0 in.2/ft)
= 600 kip/ft
ϕVni = ϕviVni
= 0.90 (600 kip/ft)
= 540 kip/ft
κ
(e)Out-of-plane shear strength
ANSI/AISC N690 Appendix N9 recommends that out-of-plane shear strength be established by conducting project specific
large-scale out-of-plane shear tests, using applicable test results, or using the provisions of the Appendix. Because no such
tests have been done for this example, the provisions of the Appendix are used to determine the out-of-plane shear strength.
The shear reinforcement has been classified as yielding shear reinforcement in Step 4 of this calculation. Comparing the
spacing of shear reinforcement with the section thickness:
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tsc
2
stt = 24.0 in.
stt ≤
tsc 56.0 in.
=
= 28.0 in.
2
2
24.0 in. < 28.0 in.
Therefore, ANSI/AISC N690, Section N9.3.5(a), will be used to determine the out-of-plane shear strength of the wall.
Vno = Vconc + Vs
where
Vconc
= 0.05(ƒ′c )0.5 tc l
= 0.05(5 ksi)0.5(55.0 in.) (12 in./ft)
= 73.8 kip/ft
l
0.5
= ζ ps Ft
≤ 0.25 ( fc′) tc l
stt
= min (Fny,Fnr)
= 150 kips
tc
=
stl
55.0 in.
=
24.0 in.
= 2.29
= 1.0 for yielding shear reinforcement
12 in./ft ⎞
= (1.0 )( 2.29 ) (150 kips) ⎛
⎝ 24.0 in. ⎠
= 172 kip/ft
Vs
Ft
ps
ξ
Vs
(N690 Eq. A-N9-20)
(N690 Eq. A-N9-21)
(N690 Eq. A-N9-22)
0.25(ƒ′c )0.5tc l = 0.25(5 ksi)0.5(55.0 in.)(12 in./ft)
= 369 kip/ft
172 kip/ft
< 369 kip/ft → Vs = 172 kip/ft
Vno
= Vconc + Vs
= 73.8 kip/ft + 172 kip/ft
= 246 kip/ft
= 0.75
ϕvo
= ϕvoVno
= 0.75(246 kip/ft)
= 185 kip/ft
Vc
The spacing requirement for shear connectors can now be checked using ANSI/AISC N690, Equation A-N9-4:
s = 6 in. ≤ c1
≤ 1.0
Qcv l
Vc 0.9tsc (N690 Eq. A-N9-4)
(18.7 kips) (12 in./ft )
(185 kip/ft ) ( 0.9 )( 56.0 in.)
< 7.82 in.
o.k.
Therefore, the shear connector spacing requirement of ANSI/AISC N690, Equation A-N9-4, is met.
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Step 8. Interaction of Design Available Strengths
The interaction of required demands needs to be limited according to the provisions of ANSI/AISC N690, Section N9.3.6. The
interaction for each element needs to be checked for all the load combinations.
This example illustrates the process by checking the interaction for one element for a particular load combination. Because element 54692 has high demands for accident thermal load combinations, the interaction of forces acting on this element for load
combination 13 is checked.
The individual demands as shown in Table A-2 are as follows:
Srx = 193 kip/ft
Sry = −75.1 kip/ft
Srxy = −67.6 kip/ft
Mrx = 4,300 kip-in./ft
Mry = 6,350 kip-in./ft
Mrxy = 223 kip-in./ft
Vrx = 61.5 kip/ft
Vry = 123 kip/ft
(a)Interaction of out-of-plane shear forces
To determine the applicable interaction equation, Vc.conc must be calculated:
Vc.conc = ϕvoVconc
= 0.75(73.8 kip/ft)
= 55.4 kip/ft
t
Because Vrx > Vc.conc and Vry > Vc.conc , and stt ≤ sc , case (a) of Appendix Section N9.3.6a is applicable:
2
5
5
⎡⎛ V − Vc.conc ⎞ ⎛ Vr − Vc.conc ⎞ ⎤ 3 ⎡ Vrx 2 + Vry 2 ( 0.9tsc ) ⎤ 3
⎥ ≤ 1.0
DCRops = ⎢⎜ r
⎟ +⎜
⎟ ⎥ +⎢
avg 2
s
ψ lQcv
⎢⎣
⎥⎦
⎢⎣⎝ Vc − Vc.conc ⎠ x ⎝ Vc − Vc.conc ⎠ y ⎥⎦
(
)
(N690 Eq. A-N9-23)
where
avg
Qcv
=
tie
net Qcv
+ nesQcv
net + nes
(N690 Eq. C-A-N9-14)
tie = available interfacial shear strength of tie bars, kips
Qcv
tie, is considered to be zero in this design example.
The contribution of tie bars to the interfacial shear strength, Qcv
However, when considered, the interfacial available shear strength of tie bars needs to be determined according to ANSI/
AISC N690, Section N9.1.4a.
Based on Figure A-1 and the commentary to Section N9.3.6a of ANSI/AISC N690:
net = 1.00
nes = 15.0
and
avg
Qcv
=
(1.00 ) ( 0.00 kips) + (15.0 ) (18.7 kips)
= 17.5 kips
1.00 + 15.0
ψ = 1.0 for panel sections with yielding shear reinforcement and yielding shear connectors
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5
⎡ ⎛ 61.5 kip/ft − 55.4 kip/ft ⎞ ⎛ 123 kip/ft − 55.4 kip/ft ⎞ ⎤ 3
DCRops = ⎢ ⎜
⎟ +⎜
⎟⎥
⎣ ⎝ 185 kip/ft − 55.4 kip/ft ⎠ ⎝ 185 kip/ft − 55.4 kip/ft ⎠ ⎦
5
⎧ ( 61.5 kip/ft )2 + (123 kip/ft )2 0.9 ( 56.0 in.) ⎫ 3
⎢
⎥
+⎨
⎬
2
⎡
⎤
1.0 ⎣(12 in./ft ) (17.5 kips) ( 6.00 in.) ⎦ ⎥
⎩⎢
⎭
= 0.672 < 1.0
Therefore, the interaction satisfies the requirements of ANSI/AISC N690, Equation A-N9-23.
(b)In-plane membrane forces and out-of-plane moments
The design adequacy of panel sections subjected to three in-plane required membrane strengths (Srx, Sry, Srxy) and three outof-plane required flexural or twisting strengths (Mrx, Mry, Mrxy) is evaluated for each notional half of the SC section, which
consists of one faceplate and half the concrete thickness, according to the provisions of ANSI/AISC N690, Section N9.3.6b.
For each notional half, the interaction is checked using the equations in principal force space using ANSI/AISC N690, Equations A-N9-24 to A-N9-26. (Alternatively, the interaction can also be checked using Equations A-N9-31 to A-N9-33. The
two sets of equations represent the same interaction surface.)
For Sr,max + Sr,min ≥ 0
+ Sr ,min ⎞ ⎛ Sr ,max − Sr ,min ⎞
⎛S
DCR = α ⎜ r ,max
⎟⎠ + ⎜⎝
⎟⎠ ≤ 1.0
⎝
2Vci
2Vci
(N690 Eq. A-N9-24)
For Sr,max > 0 and Sr,max + Sr,min < 0
DCR =
Sr ,max
⎛ Sr , max + Sr, min ⎞
−β⎜
⎟⎠ ≤ 1.0
⎝
Vci
Vci
(N690 Eq. A-N9-25)
⎛S
⎞
DCR = −β ⎜ r ,min ⎟ ≤ 1.0
⎝ Vci ⎠
(N690 Eq. A-N9-26)
For Sr,max ≤ 0 and Sr,min ≤ 0
where
2
⎛ Srx′ − Sry′ ⎞
2
Srx′ + Sry′
Sr ,max , Sr ,min =
± ⎜
+ ( Srxy
′ )
⎟
2
2
⎝
⎠
(N690 Eq. A-N9-27)
Interaction in principal plane:
jx = 0.9 if Srx > −0.6 Pno, otherwise it is 0.67
jy = 0.9 if Sry > −0.6 Pno, otherwise it is 0.67
jxy = 0.67
Srx = 193 kip/ft > −0.6Pno = −2,040 kip/ft, therefore jx = 0.9.
Sry = −75.1 kip/ft > −0.6Pno = −2,040 kip/ft, therefore jy = 0.9.
For notional half 1 (top)
Srx′ .1 =
Srx M rx
+
2
jx tsc
For notional half 2 (bottom)
(from N690 Eq. A-N9-28)
Srx′ .2 =
193 kip/ft 4,300 kip-in./ft
+
2
0.9 ( 56.0 in.)
= 182 kip/ft
=
Srx M rx
−
2
jx tsc
(from N690 Eq. A-N9-28)
193 kip/ft 4,300 kip-in./ft
−
2
0.9 ( 56.0 in.)
= 11.2 kip/ft
=
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For notional half 1 (top)
For notional half 2 (bottom)
Sry M ry
+
2
jy tsc
Sry
′ .1 =
(from N690 Eq. A-N9-29)
−75.1 kip/ft −6,350 kip-in./ft
+
2
0.9 ( 56.0 in.)
= −164 kip/ft
Srxy M rxy
−
2
jxy tsc
Sry M ry
−
2
jy tsc
=
(from N690 Eq. A-N9-30)
−67.6 kip/ft 223 kip-in./ft
−
2
0.67 ( 56.0 in.)
= −39.7 kip/ft
Srxy
′ .2 =
Srxy M rxy
+
2
jxy tsc
=
2
=
Srx′ .1 + Sry′ .1
2
⎛ Srx′ .1 − Sry′ .1 ⎞
+ ⎜
+ ( Srxy
′ .1 )
⎟
⎝
⎠
2
2
(from N690 Eq. A-N9-27)
182 kip/ft − 164 kip/ft
2
2
Sr ,max .2 =
=
2
= 187 kip/ft
Srx′ .2 + Sry′ .2
2
⎛ Srx′ .2 − Sry′ .2 ⎞
+ ⎜
+ ( Srxy
′ .2 )
⎟
⎝
⎠
2
2
(from N690 Eq. A-N9-27)
11.2 kip/ft + 88.4 kip/ft
2
2
182 kip/ft + 164 kip/ft ⎞
2
+ ⎛
+ ( −39.7 kip/ft )
⎝
⎠
2
11.2 kip/ft − 88.4 kip/ft ⎞
2
+ ⎛
+ ( −27.9 kip/ft )
⎝
⎠
2
= 97.4 kip/ft
2
2
Sr ,min.1 =
Srx′ .1 + Sry′ .1
2
⎛ Srx′ .1 − Sry′ .1 ⎞
− ⎜
′ .1 )
⎟⎠ + ( Srxy
⎝
2
2
Sr ,min.2 =
Srx′ .2 + Sry′ .2
2
⎛ Srx′ .2 − Sry′ .2 ⎞
− ⎜
′ .2 )
⎟⎠ + ( Srxy
⎝
2
2
(from N690 Eq. A-N9-27)
=
(from N690 Eq. A-N9-30)
−67.6 kip/ft 223 kip-in./ft
+
2
0.67 ( 56.0 in.)
= −27.9 kip/ft
=
Sr ,max .1 =
(from N690 Eq. A-N9-29)
−75.1 kip/ft − 6,350 kip-in./ft
−
2
0.9 ( 56.0 in.)
= 88.4 kip/ft
=
Srxy
′ .1 =
Sry
′ .2 =
182 kip/ft − 164 kip/ft
2
(from N690 Eq. A-N9-27)
=
2
182 kip/ft + 164 kip/ft ⎞
2
− ⎛
+ ( −39.7 kip/ft )
⎝
⎠
2
11.2 kip/ft + 88.4 kip/ft
2
2
11.2 kip/ft − 88.4 kip/ft ⎞
2
+ ( −27.9 kip/ft )
− ⎛
⎝
⎠
2
= 2.17 kip/ft
= −169 kip/ft
Sr,max.1 + Sr,min.1 = 187 kip/ft − 169 kip/ft
= 18.0 kip/ft
Sr,max.2 + Sr,min.2 = 97.4 kip/ft + 2.17 kip/ft
= 99.6 kip/ft
Checking the interaction for the top notional half:
Because Sr,max.1 + Sr,min.1 > 0, the interaction is limited by ANSI/AISC N690, Equation A-N9-24:
+ Sr ,min ⎞ ⎛ Sr ,max − Sr ,min ⎞
⎛S
DCR = α ⎜ r ,max
⎟⎠ + ⎜⎝
⎟⎠ ≤ 1.0
⎝
2Vci
2Vci
where
α =
(N690 Eq. A-N9-24)
Vci
Tci
Vni
Vci = ϕ vs ⎛ ⎞
⎝ 2 ⎠
ϕvs = 95
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600 kip/ft ⎞
Vci = 0.95 ⎛
⎝
⎠
2
= 285 kip/ft
Pn
Tci = ϕti ⎛ ⎞
⎝ 2⎠
ϕti = 1.00
600 kip/ft ⎞
Tci = 1.00 ⎛
⎝
⎠
2
= 300 kip/ft
And thus, from ANSI/AISC Section N9.3.6b:
Vci
Tci
285 kip/ft
=
300 kip/ft
= 0.950
α=
The interaction for the top notional half is:
⎡ 187 kip/ft + 169 kip/ft ⎤ ⎡ 187 kip/ft − 169 kip/ft ⎤
DCRNH1 = 0.950 ⎢
⎥+⎢
⎥
2 ( 285 kip/ft )
2 ( 285 kip/ft )
⎣
⎦ ⎣
⎦
= 0.625 < 1.0
The interaction for the top notional half is within the permissible limits.
For the bottom notional half:
Because Sr,max.2 + Sr,min.2 > 0, the interaction is limited by ANSI/AISC N690, Equation A-N9-24:
⎛ Sr , .2 + Sr ,min.2 ⎞ ⎛ Sr ,max .2 − Sr ,min.2 ⎞
DCRNH 2 = α ⎜ max
⎟⎠ + ⎜⎝
⎟⎠
⎝
2Vci
2Vci
(from N690 Eq. A-N9-24)
⎡ 97.4 kip/ft + 2.17 kip/ft ⎤ ⎡ 97.4 kip/ft − 2.17 kip/ft ⎤
= 0.950 ⎢
⎥+⎢
⎥
2 ( 285 kip/ft )
2 ( 285 kip/ft )
⎦ ⎣
⎣
⎦
= 0.333 < 1.0
The interaction for the bottom notional half is within the permissible limits.
Step 9. Demand Capacity Ratios and Interaction Surfaces
For checking the design of the SC wall section, the demand capacity ratios (DCRs) for all individual demands acting on every
element for each load combination need to be checked. The DCRs are calculated by taking the ratio of required strengths calculated in Step 6 to available strength determined in Step 7.
This example presents the DCRs for all the elements for just one load combination, load combination 12. Figures A-3 to A-8
show the plots for DCRs for individual demand types for all the elements of the SC wall section. The DCR for each element is
mentioned at the element location in these figures.
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(a) Uniaxial tensile forces
Fig. A-3. DCR for uniaxial tensile forces for load combination 12.
(b) Compressive forces
Fig. A-4. DCR for compressive forces for load combination 12.
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(c) In-plane shear forces
Fig. A-5. DCR for in-plane shear forces for load combination 12.
(d) Out-of-plane flexural forces
Fig. A-6. DCR for out-of-plane flexural forces for load combination 12.
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(e) Out-of-plane shear forces
Fig. A-7. DCR for out-of-plane shear forces for load combination 12.
(f) Combined out-of-plane shear demands
According to ANSI/AISC N690, Section N9.3.6a, the forces in only one element meet the criteria for interaction for out-ofplane shear forces to be considered. The DCR for that element has been calculated and plotted in Figure A-8.
Fig. A-8. Interaction of out-of-plane shear forces for load combination 12.
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(g) Interaction of in-plane forces and out-of-plane moments
The principal stresses on each notional half for each element are plotted on the interaction surface defined by the provisions
of ANSI/AISC N690, Section N9.3.6b. Because the interaction is checked for only one load combination, the data points for
the required strengths for each notional half of the elements lie in the same region, as shown in Figure A-9. When checked
for all load combinations, the data plots would have a wider spread. As seen in Figure A-9, one data point lies outside the
interaction surface, and data points for the top notional half lie closer to the interaction surface. There are a few data points
close to the interaction surface.
Therefore, the wall needs to be redesigned. One possible alternative is to use Grade 65 faceplates, which have a yield stress
of 65 ksi. The design of the SC wall needs to be rechecked with updated section parameters. Another option is to average
the demands (with ductile failure limit states) in the regions where the demand exceeds the available strength. In accordance
with ANSI/AISC N690, the demands can be averaged over a span of 2tsc × 2tsc for interior regions and tsc × tsc for connection
regions. The averaging would normally be required over localized regions of stress concentrations. If averaging is required
over a large portion of the designed wall—DCR exceed 1.0 over many elements—the wall should be redesigned. The redesign is not discussed in this design example.
Note: All the mentioned DCRs need to be determined for all the load combinations and elements, and the design needs to
be updated if required.
Step 10. Demands for Anchorage Design
The design of SC wall-to-anchorage connection is presented in Step 12. The required strengths for the connection are provided
in this section. ANSI/AISC N690, Section N9.4, discusses the provisions for SC wall connections. Section N9.4.1 discusses the
permissible connectors and force transfer mechanisms.
ANSI/AISC N690 , Section N9.4.2, provides two design philosophies for determining the required strength of the connection.
The full-strength connection, ANSI/AISC N690, Section N9.4.2 option (a), stipulates that the required strength of the connection
will be 1.25 times the smaller of the nominal strengths of the connected parts. Therefore, the individual required strengths for
connection design are:
-1400
-1200
-1000
-800
-600
-400
-200
0
200
400
400
Principal Stress, Srp2 (kip/ft)
200
0
-200
-400
Interaction surface using Equations A-N9-24 to A-N9-26
Data points for top notional half
Data points for bottom notional half
-600
-800
-1000
-1200
Principal Stress, Srp1 (kip/ft)
-1400
Fig. A-9. Plot of principal stresses in the element notional half on the interaction surface in the principal plane.
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Required uniaxial tensile strength
From Step 7(a), Pn.ten = 600 kip/ft; therefore, the required tensile strength is:
Sr.t.con = 1.25Pn.ten
= 1.25(600 kip/ft)
= 750 kip/ft
The required uniaxial compressive strength is:
Sr.c.con = 1.25(Pn.ten + 0.85ƒ′c tc)
= 1.25 600 kip/ft + 0.85 (5 ksi)(55.0)(12 in./ft)
= 4,260 kip/ft
[
]
Required in-plane shear strength
From Step 7(d), Vni = 600 kip/ft; therefore, the required in-plane shear strength is:
Sr.vi.con = 1.25Vni
= 1.25(600 kip/ft)
= 750 kip/ft
Required out-of-plane flexural strength
From Step 7(c), Mn = 15,100 kip-in./ft; therefore, the required out-of-plane flexural strength is:
Sr.flex.con = 1.25Mn
= 1.25(15,100 kip-in./ft)
= 18,900 kip-in./ft
Required out-of-plane shear strength
From Step 7(e), Vno = 246 kip/ft; therefore, the required out-of-plane shear strength is:
Sr.vo.con = 1.25Vno
= 1.25 (246 kip/ft)
= 308 kip/ft
ANSI/AISC N690, Section N9.4.2 option (b), requires that the required connection strength be determined as 200% of the
required strength due to seismic loads plus 100% of the required strength due to nonseismic loads, including thermal loads.
ANSI/AISC N690, Section N9.4.2, recommends option (a). However, if option (b) must be used, the seismic demands need to be
separately evaluated. Twice the demands due to seismic loads need to be added to the demands due to other load cases to obtain
the required strength for the anchorage connection. The connection would then need to be designed for all the individual demand
types acting together.
Step 11. Impactive and Impulsive Loading
The design of the SC wall also needs to be checked for impactive and impulsive loads according to ANSI/AISC N690, Section
N9.1.6. The procedure is not discussed in this example. This is an interior wall and will not be subject to the impact of tornadoborne missiles. However, for illustration purposes, the wall is treated as an external SC wall, and Figure A-10 is provided to
present the local response of this SC wall to flat-nosed non-deformable missiles. When the walls are checked for impactive and
impulsive loads, both the local and global effects of these loads need to considered.
Figure A-10 is based on Bruhl et al. (2015a), and the procedure is discussed in the commentary to ANSI/AISC N690, Section
N9.1.6. The figure presents the response of a typical SC wall to flat-nosed missiles. Flat-nosed missiles are appropriate for use
for typical tornado-borne missiles such as a pipe, rod or utility pole. The missiles with mass and velocity to the left of the curves
will not perforate the SC wall, while the others will. Although the faceplate thickness is 0.5 in., the figure is based on 0.4-in.-thick
faceplates. This is because ANSI/AISC N690 requires that the faceplate thickness provided be 1.25 times the thickness required
to prevent perforation.
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Step 12. Design of SC Wall Connections
The SC wall connections may be the following types:
(a) Connection between the SC wall and the basemat
(b) Connection between SC walls (or SC walls and RC walls) in the same alignment (continuity)
(c) Connection between intersecting (orthogonal) SC walls (or SC walls and RC walls or slabs)
This example presents the wall-to-basemat connection for the SC wall designed.
The types of SC wall-to-basemat connections possible are discussed in Section 11.5. This design example presents the design of
an SC wall-to-basemat connection that involves the use of a single base plate. The connection is designed as a full-strength connection. The connection should be designed for the demand types shown in Figure A-11. These demand types are:
(a) Tensile strength [Figure A-11(a)]
(b) Compression strength [Figure A-11(b)]
(c) In-plane shear strength [Figure A-11(c)]
(d) Out-of-plane shear strength [Figure A-11(d)]
(e) Out-of-plane flexural strength [Figure A-11(e)]
General geometry of the connection is shown in Figure A-12.
(a) Tensile Strength
The available tensile strength of the SC wall is governed by the resistance of the faceplates. The SC wall-to-base plate weld
needs to be designed for 1.25 times the available tensile strength of the SC wall. The force transfer mechanism considered
is discussed in Section 11.5.1 and shown in Figure A-13.
The following parameters are considered for the design of the connection. Some of these parameters need to be iterated
based on the design.
Bbp = unit width of base plate
= 12.0 in.
FEXX = 70 ksi
Missile Weight, Wt, lbs
10000
1000
100
Missile Properties
Rigid
Flat-nose
Wall Properties
tsc = 56 in.
tp = 0.50 in.*
fc′ = 5 ksi
Fy = 50 ksi
* calculations use 0.40 in. (tp /1.25)
0
250
500
Impact Velocity, Vo, ft/sec
750
Fig. A-10. Response of SC wall to flat-nosed rigid missiles.
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Fy.an = specified minimum anchor yield strength
= 60 ksi for ASTM A615 rebar
Fu.an = specified minimum tensile strength of anchors
= 88 ksi for ASTM A615 rebar
San = transverse spacing of rebar anchors
= 8.50 in.
TSC.con = connection design tensile force
= Sr.t.con
= 750 kip/ft
(a) Tensile demand
(b) Compression demand
(d) Out-of-plane shear demand
(c) In-plane shear demand
(e) Out-of-plane flexural demand
Fig. A-11. Individual demand types for SC wall-to-basemat connections.
Fig. A-12. Geometry for SC wall-to-basemat connection—elevation.
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dan = distance from anchor to the faceplate
= 4.00 in.
danc = anchor diameter
= 2.26 in. for #18 rebar
ded = distance from the anchor to edge of the base plate
= 7.00 in.
twe = fillet weld thickness
= 1.13 in.
ϕw = resistance factor for welds
= 0.75
(1) Weld tensile strength
Ae.w = weld area resisting tensile force
= Bbp twe
= (12.0 in.)(1.13 in.)
= 13.6 in.2
d1 = distance from faceplate to edge of the base plate
= ded + dan
= 7.00 in. + 4.00 in.
= 11.0 in.
Nbp = base plate length
= tsc + 2d1
= 56.0 in. + 2 (11.0 in.)
= 78.0 in.
The available strength of the weld is then:
ϕRn.w = 2ϕw(0.6FEXX) Ae.w
= 2 (0.75)(0.6)(70 ksi)(13.6 in.2)
= 857 kips on both faceplates
Fig. A-13. Force transfer mechanism for tensile demands.
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And the demand capacity ratio is:
TSC .con
ϕRn. w
750 kip/ft
=
857 kips
= 0.875 < 1.0
DCR =
Therefore, the weld is adequate. The base metal check for the welds has not been performed because the faceplate yield
strength will be less than the tensile demand for the full-strength connection design.
(2) Base plate flexural check
The base plate may bend due to the tensile force acting in the faceplate, as shown in Figure A-14. A minimum base plate
thickness is required to address this. The design is on a per-unit width basis. It is assumed that the width of the base plate
is significantly greater than the length, and therefore, the base plate will undergo one-way bending.
Bending moment in the base plate due to tension:
TSC .con San
8
( 750 kip/ft )(8.50 in.)
=
8
= 797 kip-in./ft
Mt .bp =
Then according to AISC Design Guide 1, Equation 3.4.7a (Fisher and Kloiber, 2006), the required thickness of the base
plate due to the bending moment is:
treq.m = 2.11
= 2.11
M t .bp
Fy
( 797 kip-in./ft ) (12 in./ft )
50 ksi
= 2.43 in.
A thickness of 3 in. is provided for the base plate. The flexural resistance of the base plate is computed as follows:
ϕM bp =
2
tbp
Fy
4.45
Fig. A-14. Bending on the base plate due to tension.
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where
tbp= thickness of base plate
= 3.00 in.
ϕM bp =
( 3.00 in.)2 ( 50 ksi )
( 4.45) (12 in./ft )
= 1, 220 kip-in./ft
The demand capacity ratio is then:
DCR =
Mt .bp
ϕMbp
797 kip-in./ft
1, 220 kip-in./ft
= 0.667 < 1.0
=
Therefore, the base plate thickness is adequate. Because the base plate is thick, it is not checked for prying action.
(3) Anchor tensile strength check
The design tensile demand is resisted by the anchor bars.
From AISC Specification Section B3.3, the resistance factor for tension is:
ϕten = 0.90
Gross area of each anchor:
2
π d anc
4
π (2.26 in. )2
=
4
= 4.01 in.2
Aan =
Design tensile strength of each anchor:
ϕRn.an = ϕten Aan Fy.an
= 0.90 (4.01 in.2)(60 ksi)
= 217 kips
Number of anchors needed per faceplate per ft:
TSC .con
2ϕRn.an
750 kip/ft
=
2 ( 217 kips)
Nanc =
= 1.73 anchors/ft
Two #18 anchors are required per faceplate per foot. However, the direct shear demand in the anchors, which is checked
later, requires four anchors per faceplate per foot. Anchors spaced at 6 in. in the longitudinal direction and 8.5 in. in the
transverse direction are provided on each faceplate.
Demand capacity ratio:
TSC. con
8ϕRn.an
750 kip/ft
=
8 ( 217 kips)
DCR =
= 0.432 < 1.0
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The weld of the coupler to the base plate also needs to be designed.The number of couplers below the base plate per
foot:
Nc = 8
(4) Weldable coupler weld check
The geometric properties of a Lenton weldable coupler for a #18 rebar are shown in Figure A-15.
Drc = 3.13 in.
Brc = 4.50 in.
Grc = 1.75 in.
twanc = effective throat of weld
= 1.20 in.
twanc.f = throat of fillet weld
= 0.750 in.
The total length of the coupler welds (based on AWS D1.1, Figure 2.16) is:
⎡ Grc
t wanc ⎤
Lanc = 2 π ⎢
+
2
(
)
4
cos 45° ⎥⎦
⎣
⎡ 1.75 in.
1.20 in. ⎤
= 2π ⎢
+
2
(
) cos 45° ⎥⎦
4
⎣
= 8.16 in.
And the tensile force per rebar is:
Tanc.T =
=
TSC .con Bbp
Nc
( 750 kip/ft 12 in./ft )(12.0 in.)
= 93.8 kips
8.00
The design strength of the coupler weld is:
ϕRn.w.anc = ϕw (0.6FEXX) Ae.w.anc
Fig. A-15. Geometry of weldable coupler.
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where
Ae.w.anc = t wanc L anc
= (1.20 in.)(8.16 in.)
= 9.79 in.2
Therefore:
ϕRn.w.anc = 0.75(0.6)(70 ksi)(9.79 in.2 )
= 308 kips
According to ACI 349-06, Section 21.5.1.1 (ACI, 2006), to ensure ductility:
Tanc.f = 1.25Rn.an
= 1.25(241 kips)
= 301 kips
Tanc = max(Tanc.T,Tanc.f)
= 301 kips
Demand capacity ratio:
Tanc
ϕRn. w.anc
301 kips
=
308 kips
= 0.977 < 1.0
DCR =
Although the margin is small, because this is a full-strength connection design, the anchor weld design is adequate.
(b) In-Plane Shear Strength
The in-plane shear strength of the SC wall-to-basemat connection is governed by the available shear strength of the anchors
and the friction force between the base plate and the basemat concrete; see Figure A-16.
(1) Required number of anchors
The number of stud anchors required to transfer the shear force in the concrete to the base plate is determined as follows:
Vinp = Sr.is.con
= 750 kip/ft
ds = 0.750 in.
Asa = 0.442 in.2
Fig. A-16. Force transfer mechanism for in-plane shear.
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Required number of anchors per ft:
Vinp
ϕ vQnv
750 kip/ft
=
( 0.65) ( 28.7 kips)
N SC .c =
= 40.2 anchors/ft
Forty-two steel headed stud anchors are provided per foot on the face plate. The studs are spaced at 3 in. in the longitudinal direction and at 4 in. in the transverse direction.
(2) Friction under the base plate check
The force transfer mechanism under the base plate is considered to be direct shear friction. The force may also be transferred by shear lugs, concrete bearing on rebar couplers, or other mechanisms. The shear friction contribution based on
ACI 349-06 is calculated as follows:
Alternate shear strength reduction factor (ACI 349-06, Section RC.3): ϕS = 0.85
Shear coefficient of friction (ACI 349-06, Section 11.7.4.3, base plate concrete): μ f = 0.70
Area of anchor:
Aan = 4.01 in.2
Total area of anchors:
Aan.tot = 8Aan
= 8(4.01 in.2)
= 32.1 in.2
Shear friction available strength:
ϕVn.sf = ϕS μ f Aan.Tot Fy.an
= 0.85(0.70)(32.1 in.2 )(60 ksi)
= 1,150 kips
(from ACI 349-06 Eq. 11-25)
Demand capacity ratio:
Vinp Bbp
DCR =
ϕVn.sf
=
( 750 kip/ft 12.0 in./ft )(12.0 in.)
1,150 kips
= 0.652 < 1.0
o.k.
Required width of base plate based on the upper limit of shear friction according to ACI 349, Section 11.7.5:
Vinp
N bp.req =
min ( 0.2 fc′,800 psi )
=
( 750 kip/ft 12 in./ft ) (1, 000 lb/kip )
800 psi
= 78.1 in.
Extension needed on the base plate:
N bp.req − N bp
N bp.ex =
2
78.1 in. − 78.0 in.
=
2
= 0.0500 in.
The base plate does not need to be extended to transfer the total in-plane shear of the wall.
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(3) Direct shear in the anchors check
Direct shear in the anchors is checked as follows.
Number of couplers below the base plate:
Nc = 8
Area of the anchor:
Aan = 4.01 in.2
Total area of the anchors:
Aan.tot = 8Aan
= 8 (4.01 in.2 )
= 32.1 in.2
The alternate shear strength resistance factor from AISC Specification Section G1 is:
ϕS.r = 0.90
Direct shear available strength of the anchors:
ϕVn = ϕS.r (0.6Fy.an) Aan.tot
= 0.90 (0.6)(60 ksi)(32.1 in.2)
= 1,040 kips
Demand capacity ratio:
Vinp Bbp
DCR =
ϕVn
=
( 750 kip/ft 12 in./ft )(12.0 in.)
1, 040 kips
= 0.721 < 1.0
Therefore, the anchors are adequate in direct shear.
(c) Out-of-Plane Shear Strength
The out-of-plane shear strength of the SC wall-to-basemat connection is governed by the available shear strength of the bolts
and the friction force between the base plate and the basemat concrete. The force transfer mechanism for out-of-plane shear
force demands is presented in Figure A-17.
The out-of-plane shear force demand in the SC wall will be transferred to the base plate by means of steel headed stud
anchors welded to the base plate. The force from the base plate will be transferred to the basemat by means of shear friction
in the concrete. This force transfer mechanism is the same as for in-plane demands. Because the in-plane shear strength of
Fig. A-17. Force transfer mechanism for out-of-plane shear.
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the wall is more than the out-of-plane shear strength, the connection designed for in-plane demands will be adequate for
out-of-plane demands. The combination of demands on the connectors, based on the force transfer mechanism considered,
is discussed in Step 13.
(d) Out-of-Plane Flexural Strength
The SC wall-to-base plate connection is designed for out-of-plane flexural demands as follows.
The flexural demand can be resolved into a force couple acting on the faceplates as shown in Figure A-18. The design of
the wall-to-basemat connection can be checked for these tensile and compressive demands as discussed earlier, as follows:
Mop = Sr.flex.con
= 18,900 kip-in./ft
Mop
TMop =
tsc − tp
18,900 kip-in./ft
56.0 in. − 0.500 in.
= 341 kip/ft
=
TSC .con 750 kip/ft
=
2
2
= 375 kip/ft
Because the tensile demand due to the out-of-plane moment, TMop, is less than the uniaxial tensile demand of the SC wall,
TSC.con / 2, no additional checks are required. The compression demand will be transferred to the base plate, and then to the
basemat in bearing.
(e) Compression Strength
The available compression strength of the SC wall is governed by the faceplate and concrete compressive strengths. However, the SC wall thickness is governed by shielding requirements instead of calculated demands. This is evidenced by the
DCRs for compression demands in the SC wall, shown in Figure A-4. The maximum DCR for compression demand is
0.160, which is representative of nuclear construction. Designing the connection for the full expected compression capacity of the SC wall is impractical and unnecessary, although permitted by ANSI/AISC N690, Section N9.4. Designing as an
Fig. A-18. Force couple acting on the SC wall corresponding to out-of-plane flexural demand.
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overstrength connection for the compression demand only is also permitted by ANSI/AISC N690 and is the preferred option
of the two options discussed here. The following options are available to design the connection for compression demands.
For full-strength connection design, according to Section 11.3.1, the connection, including the base plate area and thickness,
can be designed for the expected compression strength of the SC wall. The minimum base plate area required for compression bearing, and the minimum base plate thickness required for cantilever bending due to the compression reaction on the
base plate can be checked using AISC Design Guide 1 (Fisher and Kloiber, 2006). In accordance with AISC Design Guide 1,
a uniform pressure reaction can be considered on the base plate, as shown in Figure A-19. This is conservative because the
base plate reaction will be concentrated under the SC wall. Alternatively, the base plate reaction can be considered to be
uniform under the SC wall and reduced linearly to zero at the edge of the base plate. The cantilever length of the base plate
(currently at 11 in.) will govern the base plate thickness required for the limit state of yielding associated with bending
(shown in Figure A-19) due to the uniform reaction. This cantilever length can be optimized by changing the steel anchor
distance from the faceplate and base plate edge.
For overstrength design in compression, the connection can be designed conservatively for 200% of the calculated total
compression demand (instead of 200% of seismic demand + 100% of nonseismic demands) as follows.
Because the connection is designed as overstrength for compression demand, the connection design compressive force is
two times the peak compression demand in the SC wall. The compression demand can be back calculated from the peak
DCR of 0.160.
Using the available compressive strength calculated in Step 6, the connection design compressive force is:
Pu = 2DCR(ϕPn.com)
= 2(0.16)(2,510 kip/ft)
= 804 kip/ft
(1) Minimum base plate area check
The base plate is designed according to AISC Design Guide 1. Due to the configuration of the connection, the supporting surface, A2, is considerably wider than the base plate area, A1. Therefore, the amplifier factor ( A1 A2 ) is taken as 2.
Resistance factor for direct bearing according to AISC Specification Section I6.3a:
ϕB = 0.65
Area of the base plate provided:
ABP.sum = (tsc + 2d1)(12.0 in.)
= [56.0 in. + 2 (11.0 in.)](12.0 in.)
= 936 in.2
Area of the base plate required:
Pu Bbp
ABP.req =
ϕ B (1.7 fc′)
=
(from Spec. Eq. I6-3)
(804 kip/ft 12 in./ft ) (12.0 in.)
( 0.65)(1.7 )( 5 ksi )
= 146 in.2
Demand capacity ratio:
A BP.req
DCR =
ABP. sum
146 in.2
936 in.2
= 0.155 < 1.0
=
Therefore, the base plate area is adequate for bearing on the concrete.
(2) Minimum base plate thickness check (see Figure A-19)
According to AISC Design Guide 1, Section 3.1.3, the value for the critical base plate cantilever dimension, lcan , needs
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to be adjusted due to the type of connecting element. This connection can be considered similar to an HSS column,
which means that the yielding lines are located at 0.95 times the dimension of the SC wall.
Idealized cantilever length in the direction of N:
N bp − 0.95 ( tsc )
2
78.0 in. − 0.95 ( 56.0 in.)
=
2
= 12.4 in.
my =
Idealized cantilever length in the direction of B:
ny = 0 in.
lcan = max(my ,ny)
= 12.4 in.
Required minimum base plate thickness due to compressive force:
tbp = l can
2 Pu
ϕb Fy Nbp
= (12.4 in.)
2 (804 kip/ft 12 in./ft )
0.90 ( 50 ksi )( 78.0 in.)
= 2.42 in.
The 3-in. base plate thickness provided is greater than the thickness required due to compressive force.
Step 13. Combination of Demands
The full-strength SC wall-to-basemat connection is evaluated for the combined demands obtained from the finite element analysis
for various load combinations. This evaluation needs to be performed for both full-strength and overstrength connections. For a
full-strength connection, these demands need not be separated into seismic and nonseismic demands. The connection is designed
as overstrength for compression demand, however 200% of both seismic and nonseismic demands are conservatively being
considered. All the elements need to be checked for demands obtained from all load combinations. The finite elements at the
connection will have a stress concentration and there may be areas of potential stress concentration. The demands may need to be
averaged as discussed in Section 7.7. For this design example, no averaging has been done, and the demands for element 54664
Fig. A-19. Force transfer mechanism and bending in the base plate due to compression.
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for load combination 12 (Case B) presented in the following are considered. The demands are back-calculated by multiplying
the DCR calculated in Step 9 for the demand type with the available strength. The element is located at the connection between
the SC wall and the basemat. This check needs to be performed for all elements at the connection for all loading combinations.
Tensile demand:
Treq = 0.62ϕPn.ten
= 0.62 (540 kip/ft)
= 335 kip/ft
In-plane shear demand:
Vreq.is = 0.4ϕVni
= 0.4(540 kip/ft)
= 216 kip/ft
The compression demand is 200% of the peak demand from of the finite element analysis:
Preq = 2(0.16)ϕPn.com
= 2(0.16)(2,510 kip/ft)
= 804 kip/ft
Out-of-plane shear demand:
Vreq.os = 0.56ϕvoVno
= 0.56 (185 kip/ft)
= 104 kip/ft
Out-of-plane flexural demand:
Mreq.o = 0.48ϕb Mn
= 0.48(13,600 kip-in./ft)
= 6,530 kip-in./ft
Individual connector types need to be checked for the forces they transfer based on the force transfer mechanisms. The combination of demands for connector types needs to satisfy the interaction equation presented in the following. Only the applicable
demand types for the connectors have been used to satisfy the equation in the calculations that follow.
Treq Preq Vreq M req
+
+
+
≤ 1.0
ϕRT ϕRC ϕRV ϕRM
(a) Faceplate Welds
The weld of the faceplate to the base plate transfers direct tension in the faceplate and the resultant tension from the force
couple due to out-of-plane moment action. Because the demands are taken from finite element analysis, the tensile demand
may already include the out-of-plane flexural demand. However, this check conservatively considers both the demands separately. Available resistance of the weld was obtained in Step 12.
Demand from direct tension:
Treq
2
335 kip/ft
=
2
= 168 kip/ft
Treq. w.T =
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Demand from out-of-plane moment:
Mreq.o
Treq. w. M =
tsc
6,530 kip-in./ft
=
56.0 in.
= 117 kip/ft
DCRw =
=
Treq. w.T + Treq. w. M
( ϕRn.w 2) Bbp
(168 kip/ft + 117 kip/ft ) 12 in./ft
(857 kips 2) 12.0 in.
= 0.667
Therefore, the faceplate welds are adequate for the combination of demands. If the in-plane shear force transfer mechanism
considers the faceplate-to-baseplate fillet welds, then the interaction DCRw needs to include that contribution as well.
(b) Steel Headed Stud Anchors
The stud anchors are located at the top of the base plate. The anchors transfer the out-of-plane and in-plane shear forces to
the base plate. Available strength of the steel headed studs was obtained in Step 12.
In-plane shear:
Vreq.is
Vreq.an.is =
# studs
216 kip/ft
=
42 studs
= 5.14 kip/ft
Out-of-plane shear:
Vreq.os
Vreq.an.os =
# studs
104 kip/ft
=
42 studs
= 2.48 kip/ft
Resultant shear:
2
2
Vreq.an = Vreq
. an.is + Vreq.an. os
= (5.14 kip/ft ) + ( 2.48 kip/ft )
2
2
= 5.71 kip/ft
DCRan =
=
Vreq.an
( ϕvQnv ) / Bbp
( 5.71 kip/ft 12 in./ft )
(18.7 kips 12.0 in.)
= 0.305 < 1.0
Therefore, the steel headed stud anchors are adequate for the combination of demands.
(c) Coupled Bars
The coupled bars are located at the bottom of the base plate. These bars are subject to shear demand due to in-plane shear and
out-of-plane shear, tensile demands from direct tension and from the force couple due to out-of-plane moment. The available
strength of the coupled bars was obtained in Step 12.
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In-plane shear:
Vreq.is
Vreq.cb.is =
Nc
216 kip/ft
=
8
= 27.0 kip/ft
Out-of-plane shear:
Vreq.os
Vreq.cb.os =
Nc
104 kip/ft
=
8
= 13.0 kip/ft
Resultant shear:
2
2
Vreq.cb = Vreq
.cb.is + Vreq.cb.os
= ( 27.0 kip/ft ) + (13.0 kip/ft )
2
2
= 30.0 kip/ft
Direct tension:
Treq
Treq.cb.T =
Nc
335 kip/ft
=
8
= 41.9 kip/ft
Tension from out-of-plane flexure:
Mreq.o
Treq.cb. M =
N
tsc ⎛ c ⎞
⎝ 2 ⎠
6,530 kip-in./ft
=
8
( 56.0 in.) ⎛⎝ ⎞⎠
2
= 29.2 kip/ft
The interaction will be considered based on ACI 349, Section D.7:
Design shear strength of the bars
ϕVn = 1,040 kips
Design tensile strength of the bars
ϕRn.an = 217 kips
Because the tensile demand is greater than 0.2 times the available tensile strength, the interaction needs to be considered.
Treq.cb.T + Treq.cb. M Vreq.cb
+
DCRcb =
ϕRn.an
ϕVn
41.9 kip/ft + 29.2 kip/ft 30.0 kip/ft
=
+
217 kips
1, 040 kips
= 0.356
Because the interaction ratio is less than 1.2, the coupled bars are adequate for the interaction of demands.
(d) Base Plate
The base plate is subject to moments due to direct tension as well as tension from out-of-plane moment. The cantilever
moment due to the bearing reaction resulting in compression forces is also considered. The available strength of the base
plate was obtained in Step 12.
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Direct tension:
Treq
Treq.bp.T =
2
335 kip/ft
=
2
= 168 kip/ft
Tension from out-of-plane flexure:
Mreq.o
Treq.bp. M =
tsc
6,530 kip-in./ft
=
56.0 in.
= 117 kip/ft
Moment due to direct tension:
Treq.bp.T San
Mreq.bp.T =
4
(168 kip/ft )(8.50 in.)
=
4
= 356 kip-in./ft
Moment from tension due to out-of-plane flexure:
Treq.bp. M San
Mreq.bp. M =
4
(117 kip/ft )(8.50 in.)
=
4
= 248 kip-in./ft
Bearing pressure due to compression:
Preq
qreq.bp =
Bbp N bp
804 kip/ft
(12.0 in.)( 78.0 in.)
= 0.859 ksi/ft
=
Moment due to bearing:
2
qreq.bp Bbp lcan
2
( 0.859 ksi/ft )(12.0 in.)(12.4 in.)2
=
2
= 792 kip-in./ft
Mreq.bp.C =
The greater of the tension and compression moments is considered and added to the moment due to out-of-plane flexure.
DCRbp =
max ( M req.bp.T , M req.bp.C ) + M req.bp. M
ϕM bp
max ( 356 kip-in./ft, 729 kip-in./ft ) + 248 kip-in./ft
1,220 kip-in./ft
= 0.855 < 1.0
=
Therefore, the base plate is adequate for the combination of demands.
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The resulting compression force due to out-of-plane flexure is an order of magnitude less than the direct compression
demand from the SC wall. Therefore, the base plate area provided considering compression bearing due to combination of
demands is adequate.
Step 14. Connection Detailing
Connection detailing based on the design of the connection in Steps 12 and 13 is presented in Figure A-20.
"
"
"
(a) Connection profile
(b) Section A-A
Fig. A-20 SC wall-to-basemat connection detailing.
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Step 15. Design Optimization
This example presents the design of a sample SC wall. The intent was to illustrate the application of the provisions of AISC
N690. Design optimization was not the focus of this example; however, it should be an important consideration for all projects.
Some of the steps listed below can be considered for optimizing the design.
(a)The shear reinforcement for the SC wall can be optimized. Currently the tie area is 3 in.2 The tie area can be optimized
to 2.5 in.2 The tie dimensions (0.5‑in. × 6‑in. flat bars) can be optimized to provide better welding between the tie and the
faceplates. Reducing the out-of-plane shear reinforcement will reduce the available out-of-shear strength, which currently
governs the stud spacing, as shown in Step 7(e). After optimizing the tie area to 2.5 in.2, the steel headed stud anchor spacing
can be optimized to 8 in. from 6 in. currently. The interaction check for out-of-plane shear demands and interfacial demands,
as shown in Step 8, currently does not consider the interfacial shear contribution of the ties. This contribution of the ties can
be included, but experimental studies would be needed to determine the interfacial shear strength of the ties. This would
provide an additional margin of safety in the DCR calculation for interaction of demands.
(b)The current design does not satisfy the interaction requirement for in-plane forces and out-of-plane moments. However,
the design example does not consider averaging of the demands. The required strengths are determined for individual elements—here for an element size of 24 in. AISC N690 permits averaging of demands for ductile limit states for panel sections
up to 2tsc—112 in. for this example—for interior regions and tsc for connection regions. The averaging of demands can be
performed based on project documents. This averaging of demands will reduce the DCRs for individual demands and for a
combination of demands.
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SYMBOLS
Aan
Gross area of each anchor, in.2 (mm2)
Aan.tot
Total anchor area, in.2 (mm2)
ABP.req
Area of base plate required, in.2 (mm2)
ABP.sum Area of base plate provided, in.2 (mm2)
Ac
Area of concrete infill per unit width, in.2/ft
(mm2/m)
Ae.w
Area of weld resisting tensile force, in.2 (mm2)
Em.op
Model elastic modulus for operating thermal
condition, ksi
EIeff
Effective flexural stiffness for analysis of SC walls
per unit width, kip-in.2/ft (N-mm2/m)
EIeff.acc Effective flexural stiffness per unit width for
accident thermal condition, kip-in.2/ft (N-mm2/m)
EIeff.buck Effective stiffness for buckling evaluation of SC
walls per unit width, kip-in.2/ft (N-mm2/m)
Ae.w.anc Area of coupler weld, in.2 (mm2)
EIeff.op
Effective flexural stiffness per unit width for operating thermal condition, kip-in.2/ft (N-mm2/m)
FEXX
Filler metal classification strength, ksi (MPa)
Fny
Nominal yield strength of the tie, kips (N)
Fnr
Nominal rupture strength of tie or nominal
strength of associated connection, whichever is
smaller, kips (N)
Freq
Required tensile strength for individual ties, kips
(N)
n
Freq
Tie force required to resist the overturning moments, kips (N)
Fsteel
Compression force carried in faceplate normalized
with respect to its yield strength, kips (N)
Ft
Nominal tensile strength of ties, kips (N)
Fu
Specified minimum tensile stress, ksi (MPa)
Fu.an
Specified minimum tensile strength of anchors, ksi
(MPa)
Fu.sc
Specified minimum tensile strength of shear connector, ksi (MPa)
DCRNH1 Demand capacity ratio for notional half 1
Fy
Steel minimum yield stress, ksi (MPa)
DCRNH2 Demand capacity ratio for notional half 2
Fy.an
Specified minimum yield strength of anchors, ksi
(MPa)
G
Shear modulus of elasticity of steel
= 11,200 ksi (77 200 MPa) for carbon steel
= 10,800 ksi (74 500 MPa) for stainless steel
GAeff
Effective in-plane shear stiffness per unit width,
kip/ft (N/m)
As
Gross area of faceplates per unit width, in.2/ft
(mm2/m)
AsF
Gross cross-sectional area of faceplates in tension
due to flexure per unit width, in.2/ft (mm2/m)
Atie
Area of ties, in.2 (mm2)
Bbp
Base plate unit width, in. (mm)
Brc
Length of Lenton weldable coupler for #18 rebar,
in. (mm)
Drc
Bottom diameter of Lenton weldable coupler for
#18 rebar, in. (mm)
Ds
Displacement due to static loads, in. (mm)
Dy
Effective yield displacement, in. (mm)
DCR
Demand capacity ratio
DCRan Demand capacity ratio for steel headed stud
anchors
DCRcb Demand capacity ratio for coupled bars
DCRbp Demand capacity ratio for base plate
DCRops Demand capacity ratio for out-of-plane shear
DCRw
Demand capacity ratio for faceplate weld
(EI)cr-tr Flexural stiffness per unit width
Es
Modulus of elasticity of steel
= 29,000 ksi (200 000 MPa) for carbon steel
GAuncr In-plane shear stiffness of uncracked composite
SC panel section per unit width, kip/ft (N/m)
= 28,000 ksi (193 000 MPa) for stainless steel
Em
Model elastic modulus, ksi
Em.acc
Model elastic modulus for accident thermal condition, ksi
Gc
Shear modulus of concrete, ksi (MPa)
Grc
Top diameter of Lenton weldable coupler for #18
rebar, in. (mm)
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Ic
Moment of inertia of concrete infill per unit width,
in.4/ft (mm4/m)
Mt.bp
Moment in base plate due to tension, kip-in.
(N-mm)
Is
Moment of inertia of faceplates per unit width
(corresponding to the condition when concrete is
fully cracked), in.4/ft (mm4/m)
Mth
Thermal moment, kip-in. (N-mm)
Mu
Out-of-plane bending moment, kip-in. (N-mm)
Nanc
Number of anchors needed per faceplate per foot
Nbp
Length of base plate, in. (mm)
Nbp.ex
Required base plate extension, in. (mm)
Nbp.req
Required width of base plate based on upper limit
of shear friction from ACI 349, in. (mm)
Nr
Required membrane axial force, kips (N)
Nr
Maximum axial tension that can be transferred
through the joint, kips (N)
NSC.c
Required number of anchors per foot at SC wallto-basemat connection
Nu
Membrane axial force, kips (N)
Pci
Available compressive strength per unit width
for each notional half of SC panel section, kip/ft
(N/m)
Pe
Elastic critical buckling load per unit width, kip/ft
(N/m)
Pn .com
Nominal compressive strength per unit width,
kip/ft (N/m)
M pexp−c Expected plastic flexural strength of continuous
SC wall, kip-in./ft (N-mm/m)
Pno
Nominal compressive strength per unit width,
kip/ft (N/m)
M pexp− dc Expected out-of-plane flexural strength of discontinuous SC wall, kip-in./ft (N-mm/m)
Pn .ten
Nominal tensile strength per unit width, kip/ft
(N/m)
Kc
Stiffness of concrete
Ks
Stiffness of steel
cr
K xy
Cracked stiffness
sec
K xy
Secant stiffness
uncr
K xy
Uncracked stiffness
Lanc
Total length of coupler welds, in. (mm)
Ld
Development length, in. (mm)
LTR
Transfer length, in. (mm)
Lv
Length of shear span, in. (mm)
M
Out-of-plane bending moment, kip-in. (N-mm)
Mbp
Nominal base plate flexural resistance, kip-in.
(N-mm)
Mn
Nominal flexural strength per unit width, kip-in./ft
(N-mm/m)
Mo
Eccentric moment, kip-in. (N-mm)
Mop
Out-of-plane moment, kip-in./ft (N-mm/m)
MR
Resisting moment, kip-in. (N-mm)
Preq
Mreq.o
Out-of-plane flexural demand for SC wall-tobasemat connection, kip-in./ft (N-mm/m)
Compression demand for SC wall-to-basemat
connection, kip/ft (N/m)
Qcv
Available shear strength of steel anchor, kips (N)
avg
Qcv
Weighted average of available interfacial shear
strength of ties and steel anchors while accounting
for their respective tributary areas and numbers,
kips (N)
tie
Qcv
Available interfacial shear strength of tie, kips (N)
Rn.w
Nominal weld strength, kips (N)
Mreq.bp.C Moment on base plate due to bearing, kip-in./ft
(N-mm/m)
Mreq.bp.M Moment on base plate due to out-of-plane flexural
tension, kip-in./ft (N-mm/m)
Mreq.bp.T Moment on base plate due to direct tension,
kip-in./ft (N-mm/m)
Mr-th
Theoretical maximum out-of-plane moment per
unit width induced due to thermal gradient,
kip-in./ft (N-mm/m)
Mrx ,Mry Required out-of-plane flexural strength per unit
width, kip-in./ft (N-m/m)
Mrxy
Rn.w.anc Nominal coupler weld strength, kips (N)
Ru
Total required strength, kips (N)
San
Transverse spacing of rebar anchors, in. (mm)
Scr
In-plane shear force per unit width at concrete
cracking threshold, kip/ft (N/m)
Required twisting moment strength per unit width,
kip-in./ft (N-mm/m)
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Sr.c.con
Required uniaxial compression strength at SC
wall-to-basemat connection, kip/ft (N/m)
Sr.flex.con Required out-of-plane flexural strength at SC wallto-basemat connection, kip-in./ft (N-mm/m)
Sr.is.con
In-plane shear force at SC wall-to-basemat connection, kip/ft (N/m)
Sr,max
Maximum required principal in-plane strength per
unit width for notional half of SC panel section,
kip/ft (N/m)
Sr,min
Minimum required principal in-plane strength per
unit width for notional half of SC panel section,
kip/ft (N/m)
Sr.t.con
Required uniaxial tensile strength at SC wall-tobasemat connection, kip/ft (N/m)
Sr.vi.con
Required in-plane shear strength at SC wall-tobasemat connection, kip/ft (N/m)
Treq
Tensile demand for SC wall-to-basemat connection, kip/ft (N/m)
Treq.bp.T Direct tensile demand on base plate, kip/ft (N/m)
Treq.cb.T Direct tensile demand on coupled bars, kip/ft
(N/m)
Treq.cb.M Tensile demand on coupled bars due to out-ofplane moment, kip/ft (N/m)
Treq.w.M Tensile demand on faceplate weld due to out-ofplane moment, kip/ft (N/m)
Treq.w.T Direct tensile demand on faceplate weld, kip/ft
(N/m)
Srx
Required membrane axial strength per unit width
in direction x, kip/ft (N/m)
Sry
Required membrane axial strength per unit width
in direction y, kip/ft (N/m)
Srxy
Required membrane in-plane shear strength per
unit width, kip/ft (N/m)
Srxy.as
Required average membrane in-plane shear
strength per unit width, kip/ft (N/m)
Srx′
Required membrane axial strength per unit width
in direction x for each notional half of SC panel
section, kip/ft (N/m)
Srxy
′
Operating temperature, °F (°C)
Treq.bp.M Tensile demand on base plate due to out-of-plane
moment, kip/ft (N/m)
Sr.vo.con Required out-of-plane shear strength at SC wallto-basemat connection, kip/ft (N/m)
Sry
′
Top
Required membrane axial strength per unit width
in direction y for each notional half of SC panel
section, kip/ft (N/m)
Required membrane in-plane shear strength per
unit width for each notional half of SC panel section, kip/ft (N/m)
Tamb
Ambient temperature, ºF (ºC)
Tanc.T
Tensile force per rebar, kips (N)
Tci
Available tensile strength per unit width for each
notional half of SC panel section, kip/ft (N/m)
TMop
Tensile demand due to out-of-plane moment, kip/ft
(N/mm)
Tni
Nominal tensile strength per unit width for each
notional half of SC panel section, kip/ft (N/m)
TSC.con
Connection design tension force, kip/ft (N/mm)
Vexp
Experimental out-of-plane shear strength, kips (N)
Vc
Available out-plane shear strength of SC walls,
kips (N)
V
Out-plane shear strength, kips (N)
Vanc
Anchor shear, kips (N)
Vc
Available out-of-plane shear strengths per unit
width of SC panel section in local x (Vcx) and y
(Vcy) directions, kip/ft (N/m)
Vc conc
Available out-of-plane shear strength provided by
concrete per unit width of SC panel section, kip/ft
(N/m)
Vci
Available in-plane shear strength per unit width
for each notional half of SC panel section, kip/ft
(N/m)
Vconc
Nominal out-of-plane shear strength provided by
concrete per unit width of SC panel section, kip/ft
(N/m)
Vexp
Experimental out-of-plane shear strength, kips (N)
Vfr
Friction shear under baseplate, kips (N)
Vjnp
In-plane shear at SC wall-to-basemat connection,
kip/ft (N/mm)
Vjs
Joint shear, kips (N)
Vn.ACI
Nominal out-of-plane shear strength calculated
using ACI 349 code equations, kips (N)
Vni -exp- dc Expected in-plane shear strength, kips (N)
Vno-exp- dc Expected out-of-plane shear strength, kips (N)
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Vni
Nominal in-plane shear strength per unit width of
SC panel section, kip/ft (N/m)
cm
Specific heat used in elastic finite element analysis
of SC panel section, Btu/lb-°F (J/kg-°C)
Vno
Nominal out-of-plane shear strength per unit width
of SC panel section, kip/ft (N/m)
dan
Distance from anchor to faceplate, in. (mm)
Anchor diameter, in. (mm)
Nominal shear friction strength, kips (N)
danc
Vn.sf
Vrin
Required membrane in-plane shear force, kips (N)
ded
Distance from anchor to edge of base plate,
in. (mm)
Vrout
Required membrane out-of-plane shear force,
kips (N)
ds
Shear connection diameter, in. (mm)
Resultant shear demand on steel headed stud
anchor, kip/ft (N/m)
d1
Vreq.an
Distance from faceplate to edge of base plate,
in. (mm)
ec
Top plate strain
f c′
Concrete minimum compressive strength,
ksi (MPa)
f t′
Tensile stress, ksi (MPa)
hwall
Unsupported height of SC wall, ft (m)
jx , jy
Parameter for distributing required flexural
strength into force couple acting on each notional
half of SC panel section
jxy
Parameter for distributing required twisting
moment strength into force couple acting on each
notional half of SC panel section
l
Unit width, 12 in./ft (1000 mm/m)
lcan
Critical base plate cantilever dimension, in. (mm)
ls
Shear connector length, in. (mm)
n
Number of ties in transfer length region
n
Concrete-to-steel modular ratio, Ec/Es
net
Effective number of ties contributing to a unit cell
nes
Effective number of shear connectors contributing
to a unit cell
qreq.bp
Bearing pressure on base plate due to compression, ksi/ft (MPa/m)
s
Spacing of steel anchors, in. (mm)
stl
Spacing of shear reinforcement along direction of
one-way shear, in. (mm)
Vreq.an.is In-plane shear demand on steel headed stud
anchor, kip/ft (N/m)
Vreq.an.os Out-of-plane shear demand on steel headed stud
anchor, kip/ft (N/m)
Vreq.cb
Resultant shear demand on coupled bars, kip/ft
(N/m)
Vreq.cb.is In-plane shear demand on coupled bars, kip/ft
(N/m)
Vreq.cb.os Out-of-plane shear demand on coupled bars, kip/ft
(N/m)
Vreq.is
In-plane shear demand at SC wall-to-basemat
connection, kip/ft (N/m)
Vreq.os
Out-of-plane shear demand at SC wall-to-basemat
connection, kip/ft (N/m)
Vrx
Vry
Required out-of-plane shear strength per unit
width along edge parallel to direction x, kip/ft
(N/m)
Required out-of-plane shear strength per unit
width along edge parallel to direction y, kip/ft
(N/m)
Vs
Contribution of steel shear reinforcement (ties) to
nominal out-of-plane shear strength per unit width
of the SC panel section , kip/ft (N/m)
Vuin
Membrane in-plane shear force, kips (N)
Vuout
Membrane out-of-plane shear force, kips (N)
b
Largest unsupported length of faceplate between
rows of steel anchors or ties, in. (mm)
stt
Spacing of shear reinforcement transverse to
direction of shear, in. (mm)
c
Distance to the neutral axis, in. (mm)
sL
Longitudinal spacing of stud anchors, in. (mm)
c1
Factor used to determine spacing of steel anchors
(depends on whether the steel anchor is the yielding or nonyielding type)
sT
Transverse spacing of stud anchors, in. (mm)
tbp
Thickness of base plate for compression loading,
in. (mm)
tc
Concrete wall thickness, in. (mm)
cc
Specific heat of concrete, Btu/lb-°F (J/kg-°C)
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ξ
Factor used to calculate shear reinforcement contribution to out-of-plane shear strength (depends
on whether shear reinforcement is yielding or
nonyielding type)
κ
Calibration constant for determining in-plane
shear strength
εcr
Buckling strain
εsh
Shrinking strain
εy
Strain corresponding to yield stress
i
σ req
Tie stress, ksi (MPa)
Fillet weld throat at anchor, in. (mm)
μ
Ductility factor
twe
Fillet weld thickness, in. (mm)
μdd
Ductility ratio demand
ΔTsavg
Average of maximum surface temperature
increases for faceplates due to accident thermal
conditions, °F (°C)
μf
Shear friction coefficient from ACI 349
νc
Poisson’s ratio for concrete
νm
Poisson’s ratio used in elastic finite element
analysis of SC panel section
ρ
Reinforcement ratio
ρ
Strength-adjusted reinforcement ratio
ϕb
Resistance factor for flexure
ϕbea
Resistance factor for direct bearing
ϕc
Resistance factor for compression
ϕS
Alternate shear strength reduction factor from
ACI 349
ϕS.r
Alternate shear strength reduction factor from
AISC Specification Section G1
ϕth
Thermal curvature
ϕt.r
Resistance factor for tensile rupture
ϕt.y
Resistance factor for tensile yielding
ϕvo
Resistance factor for out-of-plane shear
ϕw
Resistance factor for welds
tm
Model thickness, in. (mm)
tm.acc
Model thickness for accident thermal conditions,
in. (mm)
tm.op
Model thickness for operating thermal conditions,
in. (mm)
tp
Thickness of faceplate, in. (mm)
treq.m
Required thickness of base plate due to bending
moment, in. (mm)
tsc
SC section thickness, in. (mm)
twanc
Effective fillet weld throat at anchor, in. (mm)
twanc.f
ΔTsg
ψ
α
Maximum temperature difference in °F (°C)
between faceplates due to accident thermal conditions, °F (°C)
Constant used to determine available interfacial
shear strength
Ratio of available in-plane shear strength to available tensile strength for each notional half of SC
panel section
αc
Thermal expansion coefficient of concrete,
°F –1 (°C–1)
αs
Thermal expansion coefficient of steel, °F –1 (°C–1)
γm
Material density, lb/ft3 (kg/m3)
γ m.acc
Material density for accident thermal condition,
lb/ft3 (kg/m3)
γ m.op
Material density for operating thermal condition,
lb/ft3 (kg/m3)
γs
Density of steel used for SC panel section,
lb/ft3 (kg/m3)
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ACRONYMS AND ABBREVIATIONS
ABWR advanced boiling water reactor
ACI
American Concrete Institute
ASCE
American Society of Civil Engineers
APR
advanced pressurized water reactor
ASME American Society of Mechanical Engineers
AWS
American Welding Society
BDB
beyond design basis
CIS
containment internal structure
COS
Committee on Specifications
DCR
demand capacity ratio
DIF
dynamic increase factors
DOE
Department of Energy
EFE
elastic finite element
FE
finite element
HCLPF high confidence of low probability of failure
ISRS
in-structure response spectra
KHNP Korea Hydro Nuclear Power
LIF
load increase factor
MBM
mechanics-based model
MHI
Mitsubishi Heavy Industries
NRC
Nuclear Regulatory Commission
OBE
operating basis earthquake
PT
post-tensioned
QA
quality assurance
QC
quality control
RC
reinforced concrete
SC
steel-plate composite
SMR
small modular reactors
SRP
standard review plan
SSE
safe-shutdown earthquake
SSI
soil structure interaction
TEPCO Tokyo Electric Power Company
WEC
Westinghouse Electric Corporation
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